anal sex: leading to UTI?

My fiancé and I have had anal before, always spooning. Great (aside from the pain lol), but one time I got a horrible UTI that wouldn't leave. The dr sent some studies up to the lab and it was e.colli (however that is spelled!). Anyways he did ask if we had anal sex because that was 98% what might have caused it. Ever since that I don't want to have anal in any doggie or butt up position for fear of the lub sliding down and having contamination leading to another UTI.