Pimple-like swellings in the armpits?

I get these things more frequently on both armpits, but they disappear after a month and reappear somewhere else. It hurts, and I can't apply any pressure to them. The last time I had one of these things and applied pressure, I felt pain that felt like an exposed nerve and numbed my entire arm. I put a lot of pressure on my armpit area, so maybe that's why.

You can't see it very well in the picture, but the thing is as big as my fingernail.

I can't go to the doctor for the time being, so getting checked out isn't an option unless it's something really urgent (please don't ask me why I can't go; it's because of personal problems, it's just difficult at the moment).