Sounds like SPD to me as well. He is young enough that the Occupational Therapist should be able to lower his sensitivity or at least management techniques to deal with it.

Since your son is so sound sensitive, you might want to look into some kind of kid earplugs for when you go into noise based environments that upset him.

What material is your son's diapers and clothes made of? Many of us have a lot of problems with different matterials. I have a horrible time with them. I can only wear 100% cotton, velvet, or leather. I can tolerate rayon. Most other materials burn and itch. After a few minutes I start to get hives. Clothes shopping is a nightmare for me. Not all SPD individuals have the same "safe" clothing materials so you have to test the hard way.

I recommend your son using one finger at a time to touch a material (a fabric shop probably would be the easiest for this). If he yanks his hand away quick then the material should be put on the "Do not wear list". If he starts petting the material or tries to surround himself in the material then put it on the "Wear list". Each material tested needs a different finger because sometimes it takes a while for the finger to recover from the "Do not wear list" materials. I can reuse a finger that touched a material that was on my "Wear list".

Although your son will be grumpy and/or upset after this test, the information will help you in future clothes purchases a lot and should help you figure out which clothes he will keep on him the longest.

My mother had to use 100% cotton cloth diapers on me when I was a baby because everything else caused too much pain and rashes.