Our 5 weeks old baby has been on combi bottle feeding of around half pumped breast milk and half formula (Aptamil first milk). From birth up until 4 weeks there was no problem, normal poos. Then we changed the feeding routine a bit to save us some time: bought a Nuby rapidcool bottle to make the formula, and started feeding him all formula during the night and all breast milk during the day (easier to make formula than warming up breast milk during the night and less likely to waste breast milk that he can't finish). He started having this very runny poo after the changes. First producing one massive poo explosion every day or so, no foul smelling though and still mustard colour. Went to see the GP the day before yesterday, he checked baby's temperature, listened to the chest, and checked the blood oxygen level. Saying there's no sign of dehydration so sent us back to observe for another week. Then today baby started producing a few less explosive but still very runny poo almost after every feeding, so like 5 so far today. I'm not sure if I can keep my head cool for another week going like this... though he's not showing any other sign of being unwell. Any advice pls? Thanks a lot!