@idesigay This probably isn't what you want to hear, but I think you already know the answer so I'm just going to be blunt and say it. Go and see your doctor! Assuming you live in one of the majority of countries where homosexuality isn't outlawed I can almost guarantee that they will have come across this sort of thing before so be honest about when and how it happened, as well as any and all symptoms you've had. It might be embarrassing, but doctors deal with loads of embarrassing things.
Even if you don't want to say how you think this started, still go and see your doctor! You're making a connection between a fun pokey-bum-wank several months ago, but there are other health issues that could cause similar symptoms, up to and including some cancers.
Sorry if that all seems harsh, but you need to man-up and seek medical advice, not the opinion of random forum users. Best of luck.