It sounds like you need a new doctor who has more knowledge of ADHD meds!
As Penny said, the right med at the right dose will control the symptoms without dulling his personality, but finding that medication can be difficult if your son is one of the minority who don’t do well on Methylphenidate or similar meds. Unfortunately, finding the right med can be like playing darts in the dark – you just keep trying until you happen to hit on the right one! But it sounds like stimulant-based meds (methylphenidate, Adderall, Vyvanse) may not be a good option – there are other classes of medication that can help manage ADHD symptoms.
As for the lack of hunger – my son started taking Ritalin when he was 5, so we have dealt with poor appetite pretty much his whole life. When he was about your son’s age, I explained that his medicine made his brain THINK he wasn’t hungry, but his body needed food. This meant that he had to eat his lunch, even if he didn’t feel hungry. I packed his lunch with small portions of food – 1/2 sandwich, a piece of fruit, a go-gurt, string cheese, etc – and told him that he had to eat 2 of the things in his lunchbox. It took a little while, but eventually he did get in the habit of eating on a schedule that still keeps today at nearly 30. It also helped to make sure that he got a good, protein-filled breakfast – he has had some sort of egg breakfast almost every morning since he was 6 or 7! He would usually eat a snack after school, which I kept healthy (no chips, cookies, etc) and small so that he would be hungry at dinner time 🙂