PLEASE HELP! I can keep getting UTI'S !

I am always getting a UTI consistently. Like one every couple of months. Its really starting to get frustrating. I do everything I am supposed to to prevent them but I still get them. I pee after sex, i dont hold my pee, and i drink lots of water. i just dont understand. Would like to know if anyone else has this problem and what more can i do to try and help me prevent from getting them. Advice is needed!