Cramp perut

Eh, that tightness and fullness feeling is quite common at 20 weeks, but since you're describing it as quite painful, I think it's best to check with your doctor just to be safe, they can do a quick assessment and give you peace of mind, especially since pregnancy can be unpredictable sometimes. In the meantime, try resting with your feet up and drinking plenty of water, as dehydration and Braxton Hicks can sometimes feel like that. Take care of yourself, ya!