Swollen lymph node?

I'm a 36 year old female. Five days ago I noticed a peanut sized lump under my arm. It is actually on my inner upper arm, close to the underarm.  There was a faint round red mark on the skin. It was a little tender.  The next day I stuck a needle in it (I know I shouldn't have) and a bunch of pus and blood (sorry so gross) came out.  

Now it seems to have gone a little deeper and is harder and elongated, but still about the size of a peanut, but longer.  It doesn't really hurt, unless I mess with it.  Now and then I get a bit of a twinge in that area, but I'm obsessed with it now, so maybe it is my imagination.

I have had a sebaceous cyst in the vaginal area before.  It sort of feels like that.  I don't think it is a boil, because the skin does not really seem to be involved.

Could this be a lymph node?  Do cancerous lymph nodes become filled with pus and blood?  I don't think I'm fighting off any sort of infection.  This thing SEEMS to be in the fat layers, and unfortunately I have more than my share of fat layers. I've had a couple of mammograms in my late 20's.  I had them because I ran to the doctor frantic over breast pain.  Both were negative, except that I have fibrocystic breasts.  I think he only let me have the mammograms to shut me up.  

I would appreciate your comments. Thanks.  

Susan

[Forum-M.D.-DT]

Thanks for your question and for visiting the Family Practice Forum.

I can tell you right now that what you describe is most likely a sebaceous cyst.
A sebaceous (or epidermoid) cyst is a noncancerous swelling under the skin. It is lined by packed outer skin cells. The cyst itself is filled with oil or dead cells. Under certain conditions such as stress, increased activity, mechanical irritation, diabetes, or other concurrent illness these cysts may enlarge and become somewhat tender. On occasion, these cysts will be drained by the physician and antibiotics will be prescribed. Warm moist compresses will commonly help bring these cysts

[susan502]

Thank you, doctor.  You have no idea how you have eased my mind.  My next child will be named Dean!!!!!

Susan

[Tomasello]

You are so very welcome ... and so kind.
There aren't alot of "deans" out there, your comments made me smile today.

Best Wishes
Dr. Tomasello

[majesticname]

Hello I have a question. My daughter had Non hodgkin Lymphma when she was a baby now she is 7 year old and I am noticing alot of bruises in her arm they are brown she is light skin in one of the bruise she has a bump I am scare if the lymphoma came back what should I do and what can it be. please reply. and my daughter sweating and night and she has no clothe on top.
worry mom.

[theroundround]

re:sebaceous cyst
I have been dealing with one of these in both of my underarms for more than 2 years.  One of the cyst is always very active and it get swollen pretty much all the time. I have taken antibiotics and put hot pads and it doesn't go away.  It usually hurt and sometimes it gets really irritated.  I went to the doctor and they said I had to live with it... Now I have refills on anitbiotic whenever I need it but that never takes care of it.  I also use a special soap, for less bacteria in that section.

[curious1070]

A related discussion, Lump in underarm was started.