@plz101
That, with best case (and most likely case) senerio is just a urinary tract infection. I had one 2 years ago, and your symptoms match mine. I, however, wasn't sexually active, so drink cranberry juice (LOADS of it, even if you don't like it, it helps a lot) and wait another week. Don't engage in any sex (God, I sound like my teacher) or activities. None. And if, in a week, it hasn't helped even a little bit, you NEED a doctor.
If it does work, feel safe to go to the doctor, say what you feel and he'll give you a prescription that'll make it clear up in a week or so.