Yes so normal and he can have milk (just moderate say a cup a day) it wont hurt him. I use pedilite and freeze them into pop sickles with a thing I got at the 99 cent store.
Try and use a larger size diaper over reg. diaper and a plastic cover for potty training works wonders! Also butt paste (or zinc cream & anti fungal cream) & powder should help clear it up. My daughter gets rashes bad sometimes from poop for not even 10 mins! So this works wonders also try and air him out take a plastic table cover place on floor and have him play there, and hey if he has an accident you could toss and get a new one I love the 99 cent store for these. Or walmart has some for $4.00 nice ones.
Air for maybe 30 mins to start 3 - 4 times during the day.
I hope this helps and good luck.
Bag Balm is also at walmart in the pet department. But be careful some kids with sensitive skin break out in rashes more from this I tried it gave it to my dad she was allergic to it. Great for feet too with an old sock over it over night.