What is this called?..[Medical Issue?]?

Alright,Well I don't know what to really say what this is,But I easily forget things and sometimes it be orders/questions, Like if my dad were to ask me "Please buy me a Hotdog with [Condiments]" i would forget it right when i walk out of the door?..Whats up with that? I'm one of the smartest kids at my school,but it seems i forget things ALOT?..Whats that called? And Is there any solution to fixing it?I get 7 hours of sleep at night,breakfest and alot of water.