Stomachache with loose stools

I'm at week 10 of pregnancy. Initially in the earlier weeks I was constipated. Last week I suddenly started getting stomachache with loose stools. And in recent days my stomachache tends to happen when I'm sleeping at night around 2-3am. The stomachache is very painful, feels like a bad case of food poisoning but pain usually goes away after clearing bowels. Anybody who had something similar or know why this is happening?