I’m torn with my parenting choices…

My almost 7 year old son is very hyper active and is on an IEP at school for behavioral needs more than anything else. He’s on a reward system at school and that carries over to home. He’s on a token system and has the ability to get 22 tokens a day at school. He needs a minimum of 17 for a reward. We have always had an equal amount of good and bad days. About a month ago the bad was outweighing the good. After some research, I started him on a vitamin B Complex and a super food shake. For the first time EVER he’s now had 11 good days in a row! He’s actually trying his best and making better choices. Now for my issue. The he first few times he drank the shake without problems. Now it’s like this ridiculous struggle that makes me want to scream. Tonight, he was at the table for an hour and a half whining and saying he doesn’t want it. I tried to force my hand and told him he needs to drink it otherwise he’s getting no snack or tablet time before bed. Still nothing. It escalated into me yelling and him going to bed at 7:30. It’s wearing on me because he had a good day at school and then at night it’s like I’m punishing him with this shake that has probably been the reason he’s doing better. Like what am I meant to be doing?? People I ask are like “he’s a kid. You make him drink/eat what you want him to.” That’s just not reality. How do I do this? Isn’t there like a serum or concentrated superfood super vitamin that’s not a whole cup to drink? I’ve tried to make it into a chocolate shake, hot chocolate, chocolate milk, and so on. Thanks for hearing me out. I’m just frustrated and feel like a jerk over a stupid shake.