Cutting the hair doesn't help w/ itching, unfortunately.
I would stop the oatmeal shampoos right away. Despite the belief out there, oatmeal shampoos can actually irritate the heck out of skin, esp the skin of allergy dogs. Vet Derms won't prescribe it (none that I've worked with) bc of this very issue. I'd suggest either a medicated shampoo from your vet or perhaps switch to Johnsons Baby Shampoo for awhile since it's very mild.
This is PRIME allergy/pollen season. You should go to pollen.com and type in your zip code and note the current allergens in your area -- those could be key to what's going on w/ your kiddo right now.
What is his/her age btw?
What are you feeding?
Are you giving fish oil/omega supplements? (you should)
Lastly WELCOME TO YT
!