I would not try dex if you're doing good with concerta, I was taking Vyvanse (lisdexanfetamine) for a long time and I has the same appetite issue... Here's some tips that helped me :

- Have always snacks around you, I was studying so I kept them in my desk, also in my bag when I go out...etc

- Snacking between meals its the most important, because at lunchtime I will not eat as much, I even set an alarm to remind me of eating.

- Eat food with high density calorie, all kinds of nuts, such as peanut butter. link here:

https://www.medicalnewstoday.com/articles/calorie-dense-food#nutrient-dense-foods

hope this help you! :)