Armpit lumps cause ?

Hello,

Two days ago, I woke up with sore armpits - this is relatively common for me when I begin my menstrual cycle. However, the pain has now gone away, but the lumps are still there. There are small (pea sized) and sometimes painful, sometimes not. I know the advice is to go to the doctor (I am going in just a few days), but I wanted to learn more about what possible conditions could be causing these lumps. The skin above the lumps, initially, was slightly red, but is no longer discolored. I am 22 year old female, and in excellent health otherwise. I do, however, suffer from panic attacks and hypochondria, which seems to result in me believing I have several conditions, until it is proven otherwise. I'm trying to relax, but do want to learn more about could be going on.

Please help!

-August85