I haven't but it definitely works for my 6 year old. I usually trust doctors, but the things they suggest for pooping at such a young age surprise me. Especially when babies can go many days without pooping and it's OK.
Yes we had to do this when we switched babies formula. Our ped told is 1/4 of a teaspoon, but please check with your ped bc all babies are different and my lo is a big boy! Good luck!
My LO is only about 11 pounds and that just seems so young so I wanted to see what others thought. Thankfully she ended up going on her own before I gave her any!
Haven't used it but my LO went through a period where she only pooped once every 6 days and the ped said it was nornal for them to go up to 10 days. I'm surprised your ped is so concerned after only 3 days.
Re: Milk of Magnesia for 3 month old?