What Causes Vaginal Dryness And Bleeding During Sex While On Birth Control?

hi, I am currently on birth control and I tend to have dryness during intercourse. Ive had intercourse several of times but the one time he noticed I was bleeding a little. It wasn t like my period it looked like a little bit of regular blood. I don t know if it has to do with the morning afternoon pill that I took? because this happened a couple days after that. And I don t think it is an STD either.