About two months ago, I discovered a hard lump in my armpit. It is clearly attached to the muscle - when I hold my arm straight up, it's bulging and hard. If I hold my arm out to my side, it becomes slightly "movable", just like a relaxed muscle.

The thing that makes me want to forget about it is the fact that when I flex my, erm, armpit muscles, the lump also becomes much harder, as if it's flexing as well.

But the fact that it's clearly visible whenever I raise my arm in the mirror, or so easy to feel whenever I take a shower...I just can't see a lump like that and forget about it.

But I don't have health insurance, so I've been trying to research stuff on my own. Nothing I've come across matches my symptoms - painless, clearly on the muscle, etc.

Any help/advice would be appreciated, thanks.