My 4.5yo is out of control

In OT for 6 months, made enormous progress quickly then backslid back to square one and worse.

Since about 3.5, defiant, violent, every single day. Also pooping his pants, almost every day. Just now he bit me so hard it drew blood because I took his brothers toy out of his hands after telling him twice to put it down and stop wrecking it.

We are waiting to hear back from several therapists, most of the names folks have given us don't take insurance.

He probably has ADHD, his brother who is diagnosed had the same presentation but was almost never physically aggressive. We also do a lot of telling him we know he’s a good kid and needs to work on his behaviors. Waiting on neuropsych testing.

I suspect things will get better with time/age/diagnosis but I’m absolutely exhausted.