There can be a couple different things going on. Infection can linger that long--my youngest son had a golf ball size lump under his arm that turned out to be an infection.
I can't see a lot of reason to ultrasound it, though. Did they try a good strong course of antibiotics to see if it responded to that?
Eventually they will probably have to biopsy it or remove it. I don't think you will get a lot of info from an ultrasound, personally. You may need a referral to a general surgeon, as an OBGYN is probably not going to have a lot to offer in your situation.
You definitely need to go get it checked out if only to put your mind at ease. Is it possible you have mono or some other chronic fatigue syndrome. You need to get some bloodwork done for elimination purposes. You are worrying yourself by not knowing. Knowledge is power. You can't do any course of action until you find out what this is. Keep in touch and let me know what the doctor says.
I agree ultrasound won't tell anything you don't already know: it will confirm a lump but won't be able to say what it is or isn't. At your age, breast cancer is off the list. You didn't say how big it is: if it's the only enlarged node you have and if it's only a centimeter or so, it's very unlikely to be anything serious. But if it's a definitely enlarged node, and if it doesn't recede on antibiotics, then it may need a biopsy (which is a minor surgical procedure done by a general surgeon in most cases.) On the other hand, if it's not very much enlarged and it's not clearly enlarging, sometimes it's safe to conclude that whatever caused it is not serious and it doesn't need a biopsy. Sometimes a node enlarges a bit from an infection or inflammation, and even though the process is over with, the node remains enlarged permanently. When there's uncertainty or persisting worry, getting another opinion is useful: I'd agree that seeing a general surgeon makes sense. And I'd bet a nickle that he/she wouldn't be ordering or paying much attention to an ultrasound.
I wanted to thank all of you so much. It realy helped and I will definitely be taking your advice. In response to the surgeon, the lump is sort of fibrous-y with a hard lump in the center and is an inch and a half or so in size. I also had antibiotics in the spring and it did not recede or get any better. I wanted to thank you again for your help, I appreciate everything.
please post the outcome of the ongoing case w/ the young lady with the 1-1/5" mass under her arm. i too have one that was discovered in about 04/2005 during my semi-annual oncology follow-up exam, which was and still is, approx. the size of and shape of a large poultry egg, and is directly underneath my left arm. it was discovered routinely, and i'd experienced no localized infection such as ingrown hair follicle, etc., shaving rash, etc, but, i'd had shingles on my face, by the lord's mercy, a very small localized outbreak about 1 month prior, which was treated mainly with an anitbiotic with which i wasn't familiar, and i think that the name was levaquin, very pricey for 7 days, then a poison ivy and cellulitis outbreak on strictly my arms about 2 weeks prior, which was treated with keflex and 50mg prednisone successfully, though exaggerated lymph edema and extreme sudden weight gain, was an adverse effect. i was referred to a gen. surgeon by the oncology office, whom also recommended trying very strong antibiotic regimine first, which was (i think) 850mg augmentin/potass for 14 days, also pricey, to which there was no response. i orig. had chronic bartholin gland abcess of one gland from 10/2001 to 02/2002 with e-coli and strep-b discovered upon culture analysis, which would not totally resolve despite 10 gauge needle aspirations and various recommended antibiotic regimines, so a marsupulization surgery was done 02/2002, which immediately cleared all infection and healed beautifully, but, alas, adeno and subasceous cell carcinoma was found on my surgery pathology slides, and upon investigation and study by up to 16 different medical personnel, including ob/gyn, ob/gyn oncologists, radiological oncologists, etc., after having been seen by an ob/gyn oncologist to whom i'd been referred, readical surgical treatment was recommended and carried out, to include marginal cutting to clean area out from the affected gland, partial vulvectomy, and lymph node excision by access via long left groin incision, from appox. upper left abdomen and down through left leg to approx. the knee. i healed nicely. only adverse effect has been gross edema in the areas of lymph removal. and have had routine follow-up exams conducted every 6 months which have been considered excellent up until this last one where upon the under arm mass was discovered. i am scheduled for a diagnostic surgery outpatient under anesthesia on 09/07/2005. the proposed incision is to be on the left side, chest area, just above the top of the bra line far below the armpitit in a slight curve and about 2". there is the possibility that there will be multiple node removal along with the mass, and subsequently so, a drain and receptacle installed for a short period, equal to what was in my left abdomen after the previous oncology surgery. it has been determined that there are multiple nodes within the mass already. a diagnostic mammogram, chest x-ray, and ultrasound were performed, with nothing presenting on any of them. it is hard to determine, due to the manner in which the mass has aligned itself and the surrounding tissue, ligament, and muscle, whether its been grossly enlarging since it was discovered. i have been feeling a sense of "pressure" deep up behind it internally toward the underneath of my shoulder, and it seems to be pressing on either the nerve pathway and/or blood supply to my arm and hand, and i have had some intermittent dull pain and even slight throbbing, again, deep, almost behind it, inside my under arm. coincidentally, my daughter, who is almost 21, had a small marble sized painful unresolving knot under her left under arm, (she lives in CT since 05/2003) I've been in AL, and went through pretty much the same course, had outpatient surgery to remove it under localized anesthesia, and her surgeon in her case thought it might me "misplaced or displaced" breast tissue, which makes sense because she had "knots" in her chest and under arms on and off as she went through puberty and devloped, but she won't know the pathology findings until her 2 wk. postop. visit. she states that she things that her surgeon said that upon removal, the mass was about the size of a plum! if hers appeared externally to be the size of a marble, and once removed was plum size, and NO involved node, i shudder to think of actually how big mine may really be once they get in there!!! thank you. too, i have had many a medical person since my oncology surgery exclaim to me that they'd either never even heard of anyone with my type case of oncology, or, they'd never seen a patient with it. in 02/2002 when it was discovered, even at that time the amer. cancer soc. had a tiny paragraph on it, and a r. n. called me, and said she couldn't find or help much further either, because there was almost no info. out there. no one was able to give me any odds, or projected outcome numbers, and my oncologist says he can't for the same reasons, and that his best answer for right now, was simply that with so little information, he wouldn't even discuss short or long term outcome until after i'd passed the 5 year mark. i'd just passed the 3 year mark on the day the mass under my arm was found. so, any insight in that area, would be appreciated too. many blessings and best wishes to all.