Everyone has great advice! I agree - sounds like eczema. That can be either because he is currently coming into contact with an allergen or sometimes just because. I have this and so do my twins - what a hassle. While addressing the skin issues, you should also be trying to figure out what he could be having allergy problems to or if he is just one of those atopic babies who will deal with this off and on.
I agree - I'd start simple and work my way up. Unfortunately, that didn't work for my babies. I was lotioning them 3 times a day with Eucerin, baths only once a week (because they actually dry out the skin), and it was still getting worse. It took Cortisone ointment to get under control. If you end up having to use cortisone, use ointment not cream. Cream dries things out, ointment moisturizes. And, this will need to be moisturized. The downside to Cortisone is it thins the skin. However, if you're unable to get rid of eczema any other way, just use it on the patches. It's thickened skin anyway, so it would make sense to thin out just that one part.
Once I finally got rid of the eczema, I was able to get it under control. I used Eucerin twice a day and started bathing 2-3 times a week, with Aveeno baby because that is soothing to their skin. Instead of drying babies after the bath, I immediately used lotion. That kept all the good moisture in. However, I found that Aveeno baby lotion worked even better in hydrating their skin than Eucerin. Now we're down to just one lotioning a day and they didn't get eczema at all during the season change like they had last winter and spring!
Oh - vaseline is supposed to be like the best hydrator, which is why aquafor is so good. But, for us Eucerin worked better. And, as I said, Aveeno baby worked even better for us without the stickiness. Good luck and let us know how it goes!