about 31 Weeks... cramping on left.. comes and goes.. help :(

[LB2B]

Hello everyone! I am about 31 weeks prego. I woke up this morning about 3:30 with this cramping on my left side. I at first thought that it was maybe because how I was turned... it went away.... then comes back. It was coming about 30-45 min apart. (its been a long night/day so far). Now I have them still only on my left side. Sometimes it feels like they are coming sooner. I have no idea what this is. Has anyone else felt this before? I don't want to call my doctor just yet because last time they sent me to the NICU and I knew I didn't need to be there. Any suggestions would be very helpful!