Most babies go through stages where they just don't take as much as "normal". Both of my kiddos did it, and I too found it very frustrating. But if you don't see any changes in night time sleep - starting to wake or waking more. And if they continue to gain weight, try to go with the flow
It increases/goes back to normal after a little while.
Is he around 4 months? Around that time too, my kiddos went through little blurps in their napping. I think it is related to developmental issues (rolling, etc.)
Poop thing sounds normal to me, I would consider it diahrrea if it was real watery and runny