I have a bump under my left arm pit. it's the size of a cherry. it's sore to touch. there's no rash.?

Get medical exam now: This could be as simple as a boil or enlarged lymph node but also a tumor mass depending on your condition so it requires a physician evaluation and testing to confirm and treat accordingly.

Inflammed cyst: Typically a tender bump under the armpit is a cyst or oil gland that has become inflammed by rupture. Other considerations are inflammed or abnormal lymph nodes see your doctor if it persists or worsens.