What does it mean when it really hurts to pee?

I had a major stomach ache yesterday, and was in the bathroom for over an hour because of diarrhea, and I took some motrin and alieve, and my stomach felt better like an hour later. But it started hurting really bad to pee, and everytime I use the bathroom, I can go, but once I'm almost done, it starts to really hurt, it's like a pain on my lower lower stomach, and I don't know what to do about it. Is it infection of some kind? I'm 16 years old. Does this happen to people my age? And now, it is REALLY hard to hold my pee. When I have to go I HAVE TO GO. I used to be able to hold it in for a little while, but now, I can't at all. I'm scared if I'm at school or something, I won't be able to hold it. Should I take medicine of some kind?