Stomach pain after sex

Every time I have sex, I end up with a lot of pain in the lower abdomen and it usually lasts for at least an hour. Last time when I was having sex with my boyfriend, I could feel that pain in my stomach and when he was doing it from the back, it got really bad to the point where we had to stop (that is the first time that has ever happened to me in terms of the position we were in). And usually I end up having bladder problems for like a week where I get this urgent need to pee and only a small amount comes out, there is a burning sensation and it smells like ammonia. Is this normal or is this more serious? And also what could I do to prevent this?