Burning sensation after sex?

I'm 16, I just got from my boyfriends house. We had sex and I went to use the bathroom and it stung really bad. We've had sex plenty of times and it's never stung and burned like that when I'd use the bathroom afterwards. No, we don't use a condom which we should but we don't. I got a little worried after peeing three times since we had sex earlier. Each time burned so I checked and I'm not sure what its called but the thing directly above the vaginal opening, which is also the pee hole, it was swollen and red. I'm getting worried, this has never happened before. If anyone can tell me anything please do!