serious note - Just google gum clinics like you have in your area. The websites have maps on, and opening times, the times when you can walk in on a 1st come 1st served basis, aswell as appointment only times.
Results as said above are not instant, though a lot of places they only take a week.
Tests are not as painful as they used to be, the swab is somewhat less harsh nowadays.
Tests : Pee pot - simple enough
Swab - cotton bud thing rubbed around the old peehole, and possible your crapper if they deem it required from the interview with the nurse/doctor
Bloodtest - for aids and syphillis.
Physical exam - for warts etc around anywhere you engage in sexual activity
GUM clinics are pretty discrete places and not so big a deal when you're there.
Iv been once to two different ones now and i dont see it as such a biggy anymore, the first time i was only about 16 and had thrush, which isnt really a STI

2nd time i went more as a precaution and clean bill of health - id made a few drunken mistakes and got bored of using condoms with my long term gf.
I got my all clear results on xmas eve
