Hi, I Am Worried I Have An Std Either Herpes

Hi, i am worried i have an std either herpes or genital warts. 8 weeks ago i had unprotected sex with my ex girlfriend. About 12 hours after sex i noticed small skin abrasion like a red spot which dissappeared after 2 days. No issues since then 3 doctors said i did not have herpes. However whenever i masturbate skin becomes quite red but not painful, last week i found a rash on underside of my penis which was irritating accompanied by tiny red dots. The doctor said dots were too small to be herpes, Some of the dots dissappeared even after a day but others appeared elsewhere on the penis and dissappeared similarly. These never became blisters or burst like herpes. It is of note that i am on strong antibiotics clindamycin at the moment and have been for 5 weeks. Does this sound like an std or any other form of problem such as yeast infection?