uti questions! need answers asap!

so this is my second uti, and it hurts like hell. and i am pretty sure i have gotten it by having sex on my period. the only reason i do this is because since I've been taking birth control it has made my periods super light. so light that all i use are panty liners now. so i really didn't think it was a big deal.. after all that is how i got my first one. anyway, im very concerned about being on antibiotics now. only because it lessens the effect of my birth control. so after about a week of taking the medication how long will it take my birth control to be in full affect again? should i put my new pack on hold until the anibiotics are over or keep taking my birth control on time as planned?