Hi Everyone My 8 month old has moved on to 6 ...

Hi Everyone My 8 month old has moved on to 6 month plus formula and I am having trouble finding one that agrees with his tummy. The karicare gold+ tends to make his poo so runny that it leaks out of the nappy all the time so I tried him on Nan 2 gold but that formula has constipated him so severly that he screams for half an hour trying to do poo's. I have now switched him back to the Karicare gold+ because I would rather runny poo that doesn't hurt to constipation that causes discomfort. Does changing formula like this harm them in anyway?? Has anyone had a similar experience with formula's and have any advice as any advice would be appreciated. Thanks in advance Carolyn