soy milk? What is your take on this? With whole milk, my son was having one bm a week and it was…

soy milk?

What is your take on this? With whole milk, my son was having one bm a week and it was practically killing him. So the dr told us to try lactaid. Well with the lactaid it was a LITTLE better, but he was still only going every 3 to 5 days. So then the doctor told us to try soy. I think its been better. He went a real good amount the 1st couple days of switching, but being that hes in daycare, i told them to give him soy now, but here its been 4 days again since his last bm. So im not sure if they have been or what to do about this. Last night i gave him a warm bottle of prune juice and 1cc of milk of mag. Nothing yet though.