Do you use tampons? I googled it and they also said that black discharge can be from a lost of forgotten tampon.
I have been checked for STD's and iv only been with one person soo it wouldnt be that and what kinda infection do u think it would be?
It's possible, though doubtful. It's also possible you have some form of infection/STD--see your doctor and get looked at. Make sure as well that you ALWAYS use condoms.