diaper rash

My son is almost 13 months and just about 2 weeks ago he got a bad rash.. his first rash ever. So I freaked out. It was so bad looking. Really red the first day, then kinda calmed down then turned kinda bumpy and raw, then was just extremely raw for a couple days. I did some googling and found out it may be a yeast rash. I changed his diapers from pampers baby dry (which we have used for awhile now) to the honest diapers. I dried his area after every diaper change and applied coconut oil and it was gone within 2 days. I switched him back to pampers baby dry. About 2-3 weeks later, he is starting to get the same symptoms... really red in the creases and some raised bumps. Does anyone know if this could be related to something he is eating or ?? How do I prevent this ??