I started experiencing the same thing around 28 weeks with this pregnancy. I called L&D and was told to take some Tylenol and lay down. As long as there was no bleeding I was fine.. I listened and they were right but I wasn't convinced. I'm 34 weeks and STILL have painful contractions that come and go. I'm guessing it's just because it's my second pregnancy.
Try drinking water and see if that help i was having contraction at 29 weeks due to be dehydrated and once I started drinking water they went away.