speaking from the male side i know that sex for a woman can get a bit sore after a while. and that deep penitration is probably going along the same lines. when i still had my gf she could only go an hour tops before things really started to hurt so id say it is only natural i would worry too much about it i think your age is still against but dont take that the wrong way its great u want to try such things early on. i say dodnt think on it too much.

Go see a doctor. You could have torn tissue, there aren't pain receptors up there so if you did you might not even feel it (and a wet, warm, dark place is a great place to breed infection). See a doctor, the sooner the better.

If it is an emergency, you should not be wasting your time rummaging around the net. I think I understand your post, with difficulty. I have no idea what you read online that said bleeding after sex means you have an STD. That would not happen and if bleeding started as a result of an STD, it would take a long time.

Rough sex can certainly do damage, minor or major, that would result in bleeding. Your body did not mature when you were thirteen. At sixteen, you are still growing and developing. Among other things, like continued breast growth, your vagina has not developed its full elasticity and would be subject to damage from things that would not affect completely developed sex organs. I also wonder whether you have ever had a thorough gyn exam. It is certainly required.

Bleeding after rough sex at your age requires a visit to the doctor. No matter how embarassing, it is necessary that you tell her what you were doing so that she can make some rather specific examination.

Whether or not you continue to bleed, get checked by a qualified doctor or nurse.