gassy or tummy expanding

Allie
I'm currently 30 weeks and today my stomach felt bloated and crampy, like when you have trapped gas. My back has been hurting as well, only the middle part. Is it my stomach expanding and baby growing? Trapped gas? Or something I should be concerned about?
I don't have pain in my lower back/ stomach or in the vaginal area and I feel the baby slowly move and little flutters.