Can you me immune to amphetamines, or can your body not produce dopamine?

I took adderall to help with lack of focus, in the 10mg XL (extended release) form. I did nothing. Next day, I took 2 simultaneously. Again, no effect. Third day, have ingested 30mg and no effect at all. I am not shaky, not focused, and I feel hungry and I can fall asleep in less the a minute from laying down. Please explain if you can.