Im not a parent, but I work with many troubled and disabled kids. A 4 year old with cavities is quite alarming, which makes me first think of his diet. You mention he wont eat anything but junk food? This could well be an explanation for his misbehaviour. I have seen completely out of control dx autistic, anxious and adhd children have their lives turned around by a simple diet change. It may be hard work to get him to eat your new diet but it could be worth it in the long run and for his long term health.

I have only met one child in my entire life who had cavities as a 4 year old, by 6 years his mouth was full of visibly rotten teeth, by 8 he had to get the lot removed. He apparently refused to drink anything but fizzy or cordial, the parents giving him the choice to have sugary drinks is more child abuse than your firm hand on his arm.

Well done for getting through each day, I struggle and I dont even have anyone relying on me. I admire you for trying your best and reaching out for support when you need it. All the best