What Causes Delay In Menstruation, Cramps And Spotting While Treating UTI?

in the month of January i stopped taking birth control. Within that very month i was taking antibiotics for a uti for ten days. i did not get my period. So i then started taking the pill at the times i usually start my new pack due to the fact that me and my bf don t want to use a second form of bc. My body feels completely out of wack, will it take a few months to get used to birth control again? I ve been cramping a lot and spotted a little bit today.