Welcome to YT!
What kind of brush are you using? If you run it up & down your arms, does it hurt? Then it's probably hurting him too. I sell the Madan brushes (link on my siggy) & the blue or green brush is great for sensitive pups...they'll sit still while brushing them w/this. It has beveled pins & the cushion is very soft. While brushing, the pins move thus minimal pulling & breakage of hair.
Get him used to brushing time. Put him on a bathroom counter top or table. Consistency is key & always praise him when he stands still. At this sensitive time, I just cut out any mats w/a blunt nosed scissor bc I don't want them to associate grooming time ='s ouch time. Give him yummy treats after.
