My 6 week old little boy is being combo fed with expressed breast milk and formula. We introduced more formula feeds on Monday as I can’t pump enough for him. He was previously having 1-2 dirty nappies a day but he hasn’t had one in the last 36 hours. He is feeding well, making wet nappies but does have some wind. I’ve tried some tummy massage and bicycle and he is content after passing wind with this. When do I need to start to worry about lack of poo? He is having about 1/3rd as formula and the rest expressed milk. I’ve not changed my diet or anything. TIA