Hi Air Nomad,
Stop poking yourself!
Seriously, armpits are sensitive areas, so you rooting around in there isn't helping.
I know it's hard to keep yourself from jumping to the worst case scenario, but really, what good does that do? From even your brief post, it's quite obvious that you're over-thinking this WAY too much. Just because your armpit hurts when you poke at it does not mean there's something bad going on—no swollen lymph nodes, no cancer, etc. Try telling yourself that when you start to get into these thought spirals. We're all very familiar with that sort of downward slope thinking—"what if this," or "what if that," and suddenly we're on the brink of death.
Pump the brakes! You're fine.