Amphetamine questions and harm reduction

I am diagnosed with ADHD and have been taking Vyvanse and Adderall for a few months now. For the first weeks their was no noticeable decrease in effects, but overtime my tolerance began to get weird. I have discovered that if I use Vyvanse 70mg two days in a row, on the second day the effects are halved, on the third they are practically unnoticeable. Firstly, is their any explanation for such an unusual tolerance? Secondly, I suspect that like other drugs, amphetamine tolerance scales with amount. So simply upping my dose would not be a prudent route. Lastly, I would love any suggestion for supplements that could reduce damage. I stay hydrated, multivitamins, magnesium. I know I would also be looking at antioxidants, but how often and how much? I know ALA is one of the better ones, but I have found it to be quite pricey. Any links or resources to further my knowledge would be greatly appreciated.