I've had unprotected anal sex

[marshlander]

You only really have two choices, given what you've told us. Either you make an appointment at a GUM clinic (it doesn't have to be the one nearest you) and put your mind at ease or you don't make the appointment and go frantic imagining the worst.

If you are worried about anonymity, you can give yourself any name you like at the clinic and you don't have to give an address.

While it sounds as though you probably don't have much to worry about, you can never be sure until you have received an all-clear from a medically qualified source. I'm certainly not qualified to make a call on your state of health and I guess that even the doctors and nurses we have on here would not make that call either.

Take your courage in both hands and do it. Good luck to you.