Yeah, she did. She would be really constipated for a few days, then would have an explosive nappy. It turned out that the pepti didn't suit her, so she was switched to Nutramigen AA. She has a cow's milk protein intolerance though, I'm guessing that's why your LO was switched? However, saying that, any change in formula will probably cause constipation for a while. It took about 4 weeks for Holly to fully settle on her new milk, whereas she was on pepti for about 3 months and it always caused her poo problems. You could try giving LO lactulose - Holly got prescribed it, or just a little cooled boiled water x x