Could it be that i have become resistant to my adhd medicine?

Yes: The most common situation is that you have outgrown your dose and should talk with your doc about trying a higher dose however, it sometimes happens that people do better on a different med (also a good discussion to have with your doc) as always, make sure you are getting plenty of fruits & veggies, good sleep, plenty of exercise, no screens in bed or after 11pm, consider fish oil & vitamin d.

Possibly: Possibilities include brain has accommodated to your dose and you need an adjustment. Generic for of medication is not providing you with the same amount of active medication as previous meds