So first of all, I am a 16 year old female. My boyfriend and I had unprotected sex yesterday, but his penis only entered my vagina once, and it was rough going in. It was in there for only a few seconds. Before I went to bed last night, I went to the bathroom and noticed a bit of blood coming out of my vagina. I thought it was normal at first since he probably tore the muscle or something, but I woke up this morning with a lot more blood there. I missed my period last month and I was already scared for that reason, but now I'm very scared I could be pregnant and I do not know why I am bleeding or if it is just my period. The blood is darker and runnier than usual. Please help me!
Blood is most likely from the tearing of tissue (broken hymen) and the stretching of the vaginal walls. I will give you the good news and the bad news of your encounter.
Here is the bad news...I hate to alarm you, but ANY time a penis enters a vagina, the possibility of pregnancy exists. When the penis gets erect there are preejaculatory fluid that is released to kill any bacteria from urine in the urethra. Unfortunately, that fluid has semen in it and can make its way to the tip of the penis and if it entered your vagina far enough, it is possible that some semen made its way in.
Now for the good news...most likely, you are not pregnant because despite what a lot of people are led to believe, the vagina is a VERY hostile place for foreign bodies like bacteria, and that includes semen. Semen only has a small chance of surviving in the lower regions of the vagina and has a much better chance of surviving if it is ejaculated into the vagina during sex. The further the sperm has to travel, the more likely it will die before reaching the egg.
So, most likely, you are not pregnant. I would give it a week or so and if you could get a pregnancy test (and the $1.00 one from the discount stores are probably just as good as the others for a positive or negative answer. No need in spending a great deal of money on something like that.
My opinion would be to not have sex again until you are older and possibly married, but if you are adamant about having sex again, please use a condom. Lubrication (KY Jelly is the most popular) might eliminate the roughness. I wouldn't advise unprotected sex to anyone who isn't married and doesn't want kids. You are still young and you aren't ready for kids yet.