Melatonin, how does it work?

Not at all, for me, apparently.

I take Adderall for ADD, so some nights I’m still bouncing off the walls when I should be sleeping. Both times I’ve tried melatonin to help me get to sleep, I’ve ended up not being able to sleep at all, and I’m exhausted the next day.

What am I doing wrong? It’s supposed to go in my butt, right?