Hi there
Cow and Gate comfort milk has low lactose, I had the same thing with my little man when he was on it. My HV said it is normal, it makes the babies poo smell yes, and be more runny due to the lower lactose content. Not 100% sure why, but I had the same thing when colief drops were added to the normal milk, as that also breaks the lactose down (says even on the box that poo may become the same consistancy as a breastfed babies). Trying him on another milk may clear up the runny poo, in fact it should do, and he is past the age of colic so hopefully the normal cow and gate shouldn't give him belly ache. My DD is 7 months and still poos in the night so I feel your pain lol!