I went to L&D for that stomach and back pain too on Wednesday. I'm 31 weeks and turns out I was having contractions due to dehydration. It went away with the IV they hooked me up to
If it went away after some rest and drinking water, you may have just been dehydrated. If it happens again and doesnt go away with a change of activity or drinking fluids, then i'd call but otherwise i wouldnt worry too much. Maybe could bring it up to your dr at your next appt?