My 1,5 yet old son has been constipated, cries when he has to go and strains trying to hold it in. Paed said to give movicol half sachet twice daily (adult dose) this helps and I give him a balanced diet, trying to give prunes, lots of veg and fruit. My question is, his on Nido formula, I changed to similac just in case it s the milk causing it..is that a good idea ? How much milk formula should he be drinking per day now?