Cyst or STI? Sudden change in size and appearance

I’ve had this bump on my penis shaft for awhile now and I can’t really figure out when it first appeared but the size and appearance of it has changed in the last 6-12 hours. The thing started off as a small smooth bump but has turned into a yellow pimple like cyst.

I’m not sexually active at the moment and the last time I had sex was January 1st 2021.

The pimple thingy doesn’t hurt (and I haven’t felt discomfort in the past months). could someone give me advice on what it could be and if I should see a doctor?

looks like a large pimple, cyst
leave come to a head
give it a squeeze a hard core should come out if its only pus leave it a couple more days
it will probably leave a small hole but that will clear up