contractions.

Okay, this may be dumb but I'm a ftm and 35 but have been measuring big. I have been having some cramps and some pain. The only way to describe it is like when you go running and you haven't ran in a while and your sides hurt. I have that feeling like the tightening around my belly. I have a high pain tolerance and over look a lot of things because of it. Could anyone tell me what contractions are like?