Can cows milk cause constipation? Harrison is constantly constipated. We’ve changed so many things…

Can cows milk cause constipation? Harrison is constantly constipated. We’ve changed so many things in his diet but nothing has worked. The doctor has him on laxative everyday and he’s been on it for a few months now. I did mention cows milk to the doctor as it seemed to start when I started moving him onto cows milk but he didn’t seem to think that’s what’s causing it. I was speaking to someone today who said cows milk could definitely be something that’s causing it. He loves drinking milk and he still has 3-5 bottles a day😩 Could this be causing it? Should I change him over to another kind of milk? Is it safe to do that? I really want to figure it it’ll out as I don’t like him being in laxative constantly.