can anyone relate ? sorry tmi..

Ok so I'm 21 weeks now, since probably about  14 weeks I have had random but daily stomach cramps. Most night it wakes me from sleep. It feels like gas or diarea cramps but I don't have to fart or go restroom... It goes away after a little bit . I have made sure I'm not constipated and to drink a lot of water but it worrys me that it hurts so bad. This is my third pregnancy and I've never experienced this.. My ob kinda brushed it off as normal but I don't think he understood I'm not sure. Any body else ? Advise please ?