Stomach super tight and uncomfortable after sanding dresser?

I'm 31w2d; keep in mind my SO is in the navy and stationed in another state, so hes not psychally here to help set up the nursery. So I was just sanding the baby's dresser because I'm painting it and I'm afraid I put too much pressure and strain on myself.. my whole stomach is tight and cramped up now😞. Like those cramps you get from running, only its under my ribs and on the sides of my tummy. It feels tight as well, and some minor pain when I move around too much. I was sitting on the floor painting and sanding, I only got around to two drawers, and didn't even finish them because the tightening began and my back began to hurt. Also feeling a little nauseous too. Whoever, she's moving around in there a lot right now. Idk if this could be serious or harmful or not, I didn't thing sanding something would put too much strain on my body or the baby at all:/