Scared don't know what it is..

Okay so last night I noticed I had a small bump under my armpit, and it started hurting every time I put my arm down.. I had this once before but it went away.. but today my armpit looks a little swollen and never had that before.. I kept touching it last night... but now I'm scared because my armpit looks swollen.. my boyfriend said its probably an in grown hair from shaving... have any of you ladies had this before and what is it???