I'm going to bump this up because I've been feeling the same for a bit now and curious what the ladies have to say.
Actually, all through pregnancy, women have contractions randomly, but they don't begin to feel them until the baby gets bigger. Google Braxton-Hicks contractions for some useful information.
I am also 28 weeksand I have that too but I went to the ER and they have me shots to stop the contractions I am 1cm dialated and feel like baby is going to fall out :( I have a lot. Of pressure in my v!&!Π@ so my doctor is keeping a close eye because. Of my past history of preterm labor!! Hope this. Is not your case but I would get check out!! To be safe!!