How long is Adderall supposed to last?

I mean how many hours is it effective during the day? I usually take 1 pill at the beginning of the day like at 6 am and by 1, it seems like it wares off because i fall asleep in that cl. I really don't know what kind I take. I know that it's not Adderall XR, it's a little blue tablet that has AD on it and numbers on the other side. My doctor told me mom to only give me 1 a day. So what can I do to make it last longer? Should I take half at the beginning of the day and take the other half at 1?