Def. try peeing before and after sex, especially after.
also, do not hold it when you have to go, this is really bad for you.
Try drinking lots of water and avoid soda. drinking lots of water flushes you, so its not only good for uti's its good for general health as well! Cranberry juice is good too.
If you are getting them all of the time then invest in some "urinary health" pills which are just cranberry pills.
I have the same problem, so I understand. I had NEVER got a uti until I got with my current bf about a year and a half ago. He has a really big....you know! My gyno said this could have something to do with it, bc sometimes he puts pressure on my bladder during sex, so if your man is well endowed then this could also be a contributing factor.