What Causes Bleeding During Intercourse?

The past few months I have been bleeding during sex. I went to my gyno and he put me on antibiotics. It didn't help. I am 45 and have also been having thyroid problems. I am hyper thyroid and having been taking an anti-thyroid medication which has caused me to go hypo. I did not start noticing bleeding problems until I started having thyroid issues. Could this be the problem? The bleeding is not heavy and I don't bleed after sex.