What’s wrong with my baby??

I have a huge concern in regards to my babies neck. His neck is extremely red ( like a rash) we already talked to his dr about it. The dr said it could be because no air reaches that area. My baby is 3 months old for reference. He scratches it with his nails or so it seems, it just seems itchy and irritated. I do my best to keep it clean and dry. I bathe him frequently and moisturize the area. I also have been applying A+D ointment for rashes and skin protectant with my doctors okay. What else can I do?? Or what could be causing it? Help please