Sounds like you are a hypochondriac to me.
Don't get me wrong, I am not slagging you, but I really doubt you have anything.
I remember one time thinking I had some sort of STD, I even had a slight discharge. I went to the doctor, got it checked out, can't remember what they called it, but it was NOT an STD, it was something else. Turned out to be nothing.
That being said, certain types of STD's can live in the back of the throat, including syphilis, so there is always the risk.