I noticed a similar type bump back in September... I was so scared, thinking it was a lymph node. I went to my primary MD and was treated for folliculitis and sent home with antibiotics. After a repeat situation (these underarm lumps turned to the size of a golfball) I went to my derm and was diagnosed with hidradenitis suppurativa. It is in remission now, thankfully with high doses of tetracycline.

Please, contact your dermatologist and have it diagnosed, you'll be glad you did.:)