Last night me and my boyfriend had sex, after awihle it began to hurt and there was blood and also i felt like I was cut, when I go to the bathroom and pee it stings. And I have been having stomach pain at random times, after I eat, when i sit down, or lay down, i have random pain. I'm also on a birth control shot, is there any explanation for this?
Often, the feeling of being "cut" is actually what happens. If there isn't quite enough lubrication upon penetration, that "pulling" can often lead to a scrape/cut which will be irritated and burn during sex, and after. The only thing that can heal it, is for it to be left alone. You'd need to ask yourself how long you've been on that shot, and if complications like this have been going on ever since. If the problems are since the shot, then you'd need to talk to your doctor. How long have the pains been happening?
What kind of stomach pains? Lower, upper? Shaken up due to all the motion? Gas pains? Blunt pains? Sharp pains? Lower abdominal cavity pains that most refer to as "stomach"?
Repeated lack of lubrication can cause skin irritation and rub things raw. Though some are into the "raw sex" and not meaning without a condom, it is not advised to try to force intercourse if things are too 'dry', as things like this can happen. However, considering urine does not come from that area, it could be an infection, or it could just be from not-so-gentle oral sex that has caused the area to be swollen and irritated. If it doesn't clear up within 48 hours, you might check with your doctor.
Try to be a bit more specific about things, or ideas you have about "why" it might be, and I'd be able to answer your questions without generalizing as much.
If your partners penis is fairly large, and there is rough sex involved, that can bruise and cause uncomfortable feelings of stomach upset. Humans will actually hurt themselves, or strain themselves badly when sex is involved. Because of the way the brain works, they may feel little or no pain during the moment, but afterwards can suffer severely.
On that same note, if things 'begin to hurt', you should always stop immediately because something is probably wrong.