UTIs while pregnant

I am 21 weeks. I have had a UTI Come and go almost my entire pregnancy this time. I didn't have this issue my last pregnancy. Anyone know why this would keep happening?? It is driving me crazy. Im not doing anything different than normal and I don't usually have an issue with UTIs unless I don't pee after sex which I'm on pelvic rest so that isn't happening anyway and hasn't in months. Im so frustrated. Dr can't give me any reason for it either other than "sometimes that happens".