Something I've noticed is that not taking my ADHD medication (which has varied in medication as well as dosage throughout my life) is what leads to impulsive eating, going through snack food like crazy. My pediatricians and later doctors, have said that the medication typically does lead to appetite loss. I know the feeling that the medication will just magically sustain you through the day. That, coupled with the high increase in physical activity, is what has contributed to your weight loss. You do need to make a conscious point to eat at lunch, even if you don't feel hungry, just to maintain weight.

I hope this helps you!