A common reason for cramping around this time of pregnancy is due to dehydration. Make sure you drink plenty of water 8-10 big glasses a day. If you start to notice a pattern with the cramps, like they are coming every few minutes, then call your Dr. right away. Otherwise, I wouldn't worry too much about it.
Hello, I am 34 weeks prego and i am having the same problem. I asked my doctor about it and he told me my uterus was getting ready for labor. He also recommended i drink a big glass of water if I did cramp and that if i got that feelign more than 5x a day to go to the hospital.