Can STD/STI still be detected if i have self medicated with antibiotics ?

I had unprotected anal and oral sex whilst abroad 10 days ago with another guy. I know I was a fool but in the excitement of the moment it happened. Havent had sex for a year of more with another person. About 3 days later I developed a rash on the glans of my penis. A small purple lump on the tip near the opening of the urethra. Burning whilst peeing and creamy white build up during the day under forskin. I am meticulous about cleanliness showering twice a day and keeping my bits clean. As i was abroad I couldnt see a GP or go to a Gum clinic. I got my hands on some doxycycline and took 100mg twice a day for 4 days. Then started amoxyciline 100mg 3 times a day - am half way through those. Also used 1% hydrocortisone cream on the glans. Things are clearing up and the rash and bump has gone. Am back home in UK, should I still go to a clinic and get tested for an STD/STI or will it now be a waste of time?

I think you should go see a doctor

Just tried to book an appt with one of the local sexual health clinics where I live. They told me the next available appointment isnt available until 10th July. Thats nearly two weeks away. I am also working away then so couldnt make that anyway. I have ordered a home testing kit which should arrive tomorrow. Might be in Birmingham end of the month and I know they have walk in clinics there. May try one of those.