A couple of months the ago I had a blister type lump near my anus for about 2 days it wasn t painful and it kind of just popped on its own and went away as a blister would at first i thought it was just from sweating because i am an athlete and my skin does not like spandex which i do wear every day A couple months prior to that I had brief unprotected skin contact near my anus no penitration or seminal fluids were involved. Should I be concerned or does this have something to do with skin sensitivity or sweat glands. The bump never reoccurred. I was tested for stds 3-4 weeks after I became sexually active which was about 3 months before the bump and everything came back clear since then I ve donated blood had my blood looked at in the hospital from a case of pericarditis and a blood culture and a couple other blood tests from pericarditis a second time about a month ago.