Ugh, I'm sorry that is happening! That's a big pain and mood killer, I'm sure. Things that can cause this include polyps either on the cervix or uterus but you are a bit younger than women who usually get those. But never say never, they do cause bleeding from sex. There is something called cervical ectropion which you are the right age for. This has to do with your cervical cells and while they normally grow inside your cervix, with this they are growing on the outside. It's not dangerous or anything! But it causes the blood vessels on the cervix to dilate and become inflamed and they bleed. Taking birth control pills increases the odds of this. Trauma (rigorous sex) can also cause it if you are doing this every time. ? Cuts, scrapes, tears happen. There are things that happen to women that are menopausal or post menopausal but I won't list those because you are too young for that. Make sure you are well lubricated during intercourse, obviously. And this is something that I'm not sure you tested for which is STD's. When you visited your doctor, did they test for those and also swab your discharge? Things like trich can cause it. The last thing is endometriosis but I would imagine you'd have other symptoms if that was the case. Did you tell your doctor about the bleeding and did they have suggestions? Anyway, hope this helps. Let us know how you are doing!