Hello Thanks for writing to us with your health concern. See, you have been using Nan Pro for quite some time. So the brand is less likely to cause loose motions. During the transition of weaning your child from breastfeeding to formula, it is very common for infants to experience diarrhoea and loose stools. This is also the time around which teething starts to happen. This is another reason for the loose motions. Nan Pro 2 is heavier and slightly difficult to digest compared to Nan Pro 1. Have you consulted your doctor about using the formula feeds ? Are you properly boiling his drinking water ? If you are bottle feeding him, meticulous sterilization of feeding accessories is also a must. Lack of sterilization also can lead to such infections. If it is not stopping inspite of antibiotics, try breastfeeding him for a few days till he stabilizes. All the best. Take care.