First, I would like to congratulate and encourage you for the active role you are taking. I know too many parents who could learn by your example.
Every person needs to learn how to motivate themselves and find interesting activities to pursue, whether ADHD is involved or not. Maybe you can help your child identify activities they enjoy on their own. They will need this skill when they get into preschool or kindergarden. It might be helpful to observe your child when they are alone, when they see no one nearby, to notice how they spend their time. Some kids stop entertaining themselves when others are around because they learned to do that.
Alone-time and being a little bored can be a powerful tool to boost creativity and initiative.