Having trouble peeing?

On Sunday I had to go to the er because I couldn't pee. My bladder was full and I felt like I had to pee really bad but nothing more than an occasional trickle would come out. At the er they put in a catheter and emptied my bladder and told me my uterus was blocking my urethra and if it happened again there was nothing they could do but put in another catheter and if it became a recurring problem I would gave to leave it in. I saw my ob and he said the same thing about my uterus blocking my urethra and that it would get better ad i got further along and my uterus rose more. Since then it hasnt gotten nearly as bad as it was the first time it happened but there are times when I can't pee normally and at times it takes almost an hour for me to empty my bladder. Has anyone had this happen? With my first pregnancy I used to have to lean forward to empty my bladder but I never experienced anything like this. Does anyone know of anything I can do to keep this from happening? I really don't want to end up back in the er. It was a miserable experience and the er is expensive! Everyone I've told this to says they've never heard of such a thing but my ob and the dr and nurses at the er acted line it was normal.