6.5 year old - social problems

[RKBNY]

My son is in first grade, and he was formally diagnosed with ADHD last year, but I've suspected for several years that something is going on. My son is very smart - he's on track or ahead academically - but he's having a very, very hard time socially at school. Whenever I'm around his school, I hear the children whispering things like "e Look who's here. Let's stay away from him." His teacher also told me that nobody wants to sit next to him because they think he's mean. And, he has trouble listening to grown ups. I genuinely don't see him as mean or bad - he's just so impulsive and can't keep his body to himself. He really cares what other people think and wants to be liked, but he's starting to refer to himself as a "bad boy" and a "bully." It's breaking my heart.

Last year he went to group play therapy, one on one therapy and private OT but it was all so expensive. We got him on a 504 plan, and he now has OT at school and sees the school psychologist. I also took him off gluten, which I do think helps a bit. What else can I do?! We are trying to do as much as we can without putting him on meds, but I really fear this is messing with his head and making him hate himself. I'm exhausted and just generally very sad.

Any advice is appreciated.