I'm a 24 male, and over the last year I've been getting these weird pimples on my arms primarily but also on my chest and shoulders. They start off like a small pimple head with an inflamed red circle around it, like I've been bitten. The inflamed red circle then goes away and the pimple gets bigger. Eventually it becomes puss filled and I usually end up popping it. Healing takes a very long time, usually 2 to 3 weeks. It heals to a dark purple circle. I have gone through a course of Flucloxacillin, but because the pimples come and go through stages, I'm not sure if the antibiotics had an effect or not. What do I have?
I can post pictures if that will help.