Hi standra,
I think that you should see the doctor if the lump doesn’t disappear on its own within a weeks or so, or if it appears to be getting worse.
There are many, many causes of underarm lumps, and the vast majority have nothing to do with cancer.The most prevalent cause of a lump in the armpit is infection. An infection can be localized to the armpit itself (perhaps a nick from shaving) or it can be more widespread.. you may also have a boil or abscess just under the skin.
If it's a swollen lymph node,this could be caused by an infection somewhere in the body.As you can see,it's really impossible to tell you what this lump could really be, and I think that you should make an appointment to see your Doctor for a clinical breast exam,just to make sure that it's nothing more serious.
Best wishes...and take care.