stomach tightened after walking around

I accompanied my husband to a fishing show (we both went fishing before we got pregnant) which I thought was just a small show but turned out to be a couple of exhibit halls big. As we were walking around, I felt my stomach tighten and it felt really hard but didn't think anything of it since we also just had our meal but it got more uncomfortable as I walked more so I told him that I would sit and rest while he goes on with the fishing show.
Was it right for me to be worried? We are only 14 weeks pregnant. I also feel the tightening sometimes when I wake up and have had a stressful dream. Does anyone know the reason this happens? Is it normal or should I be worried?