poop 💩

I could smell a meaty smell.. like raw meat that's turning a bit bad, checked my little ones nappy and he'd pooped! Smells strongly of raw mince! Anyone know why this could be? He's bottle fed, has trouble with constipation, but has been going regularly for around a week or so after doctor prescribed him movicol once every two days.. but only tonight it smelt like this! He's 15 weeks old x