Look up sexual transmitted deseases. There are so many and they will also have the symptoms. Since you have have had sexual deseases before (too many) you should have learned something by now, unless you don't care about living a long and healthy life. As a politician said, " change". If you think about it, you are probably worring yourself and your imigination too much. Please let me know if you find a solution to your problem.
By the way, how old are you? Seems to me you are old enough to ask good questions, but you already know alot of the answers yourself. Good luck and keep your pants up for a while until you can figure out if its worth all the risks you are taking.