Hi. I am 19 years old, and usually in fine health. Don't smoke, drink occasionally. A few months ago my girlfriend and I (neither have had unprotected sex with anyone else) noticed a small lump on my left buttock, towards the top, and midway across. I thought nothing of it, and a few months later I noticed it again. I'm not sure if in the elapsed time it was gone, I may have just forgot about it and didnt notice it again for a while. It is around a centimetre in diameter (not formally measured), uncoloured, firm/hard, and only painful if it is rubbed or pressed hard, so normally not painful at all. I'm unsure as to whether it is growing, some days it seems to be different sizes to other days (the 1cm is probably the best average). I assume it is some kind of infection but I don't really have any reason to suspect this. Thought I should probably ask. Can ayone diagnose me? Thanks...