he really doesn't seem sick though and he just ate and was fine so I'm thinking it's the poop thing

There's a horrible stomach bug going around

I'm thinking he needs to poop because he hasn't today but he doesn't ever normally eat so little and not get hungry

could just be a little bug. try giving him some pedialite, and if it gets worse, he doesn't eat tomorrow or he spikes a fever; call the doctor. but trust your instincts too, if something doesn't seem right; take him in right away

acid reflux?