s formula

So my son is 10 months old, when he was a newborn we had to switch him off the similac  adance and go to the soy and that did not work either. So we ened doing to the sensitivity and it finally settled his stomach, I go to my WIC appt yesterday and the lady tells me I can put the advance and sensitivity together (half and half) does anybody do this? Will this hurt his tummy at first like a newborns?