Milo is getting more teeth
So the word on the street (from a mom I know) is that the diaper rash is caused by excess acidity in his urine, which is a by-product of the whole teething thing.
When the new teeth come in, the baby drools more and swallows it, which leads to more diarrhea, which makes his bum sore. Either than, or the acid comes from the newly formed tooth.
I can vouch for the acidity thing -- I've certainly noticed a stronger smell coming from his wet diaper in the morning.
So, before he's gone forever, here are a few more pics of still mostly toothless Milo. Seven teeth and counting. Actually, I haven't been counting. I'll count tonight when he's in the bathtub.