nspeth
glad to hear your son is doing ok, I got scared with that E.coli thing.
I wanted to tell you that my son too has had some rashes coming and going, the doctor told me it was just sensitive skin, but later on I found out he was allergic to the ecological diapers. Now in the summer I just keep him the most possible without anything.
About the sun, don't be afraid. My son is 22 months, but he stays every day under the sun at noon without sunblock and never gets even red, he's very white sensitive skinned but the sun doesn't do any harm to children really, on the contrary. You can just wet his hair every now and then, and that's enough. He needs a lot of sun.
Another thing, don't use any commercial products for the skin of your baby, if you look at the list of ingredients it is a no no for sure. Just go with plain good oil, and only if very necessary. It is better to let the skin find its balance by itself. Keep him naked in water and sun and that's all he needs. Many times the skin just needs to be hydrated more than nourished. The vit.D produced by sun-exposure is the best protection for the skin.

About oatmeal, maybe your son is not really allergic, maybe he's just not ready. Have you tried rice-flakes? you can also consider keeping him on fruits and vegetables only, for now or forever. Try carrots and apricots, which would be good also for the skin. You can also boil some fruit in water, eat the fruit and give him the water. He could like to have some minerals replenished if his poopoo is on the wet side. Best of all, go ahead with your milk, he's a lucky boy to be still nursed by you!