Bladder and stomach pain

Every time I'm ready to start my period, I get a bladder infection. I don't know if it's from using tampons or from sex(I always pee afterwards or taie a shower). Yesterday I felt a sharp pain in my kidneys and today I'm off work because I've been in a lot of pain. I've been drinking water and cranberry juice since it started. My period isn't supposed to come for a couple days but it always seems like this happens right around then. Help!!!