My son has been on whole milk for over a month now and I've noticed that he has more poops 2-3 a day…

My son has been on whole milk for over a month now and I've noticed that he has more poops 2-3 a day . They have changed in color and smell TMI it's yellow and very soft sometimes border line watery.If he farts he will poop or a small bit will come out , he's gassy as well more often & has a permanent diaper rash. I took him in and his pediatrician said it's his body trying to adjust to being on whole milk, that I can try lactaid but if that didn't work with him he needs to go back to whole milk 🤔 . His diaper rash is constant from all the poop he's doing some days it's worse than others but I find myself going through diapers and cream like crazy ! Has any mom have the same issue ?? Please help !