UTI? Or Pregnant?

Lena
Hi! I've been on the pill for about 3 months and 2 weeks, recently me and my boyfriend have started having unprotected sex, for the past couple of days I've been having a burning sensation when I pee and I find that I need to go more often then usual, last night my lower back started hurting. I take the pill every night around 10. Can someone please help?