I had the same issue. I talked to my doctor and she said that the bleeding was most likely from lack of lubrication (natural or otherwise) during sex. Some birth controls can cause a woman to not get as "wet" during sex. Vaginal dryness can result in tears in the vagina during sex, which results in the bleeding seen afterwards. It can also result in pain and yeast infections. My doctor recommended using a lubricant or having more foreplay before sex to help with the dryness, and it seemed to work. You might want to try doing this, especially if you are not using lubricated condoms. I know that the internet says that vaginal bleeding can be the result of an STD, but if you are in a monogamous relationship and neither of you had an STD before entering the relationship, you really shouldn't have to worry about that problem. So many different things can cause vaginal bleeding, so you should definitely call your doctor and get his/her opinion.