Sorry, do you mean to say that you’re taking 3 5mg Adderall tablets in the morning, before lunch? You’re meant to space those doses out over the course of your day. I’m on Ritalin instant release (until Monday), and I take my pills at 8:30, 12:30, and 4:30.
You’re actually technically overdosing yourself (with regards to the dose you’re supposed to be taking) by taking them ALL before lunch time. The idea is to always have 5mg of adderall in your system. You’re not taking one-a-day pills, which last for 12 hours, you’re taking short-acting, short-effect pills. It’s not surprising that the effect is gone by lunchtime.
As long as you don’t take a pill after 7:00pm, you’re fine.