I feel a UTI coming on, what now?

I keep getting these stupid things like once a month since I got pregnant. I just got off a week long regimen of antibiotics for a bacterial infection and the day after I stop I feel like I'm getting a UTI. It's not from because I'm not allowed. I pee whenever I need to and don't hold it so what's causing these UTIs? Can I do anything to prevent them? I drink about 80 oz of water every day with cranberry juice occasionally.