What Causes Cramping And Pain In Vagina?

well i have recently had my baby five weeks ago. And at two weeks i had a UTI and i have been sexual active since. He wore a condom but after he stuck it in my vagina. He has done this up to three times. My question is i have been cramping like a menstral starting with somtimes stinging pains on my vagina for the past three days. Causing to be uncomfortable also in my lower back what could be the problem and what can i do to stop the pain ive tried over the counter meds.