Adderall XR and sleepiness?

I am on addreall Xr 20 mg I have been on it for 3 weeks and the first week and a half I was sleeping on average 7 1/2 to 8 hours a night which was great after that I noticed I was really tired in the morning and it took a while for me to wake up after I took my adderall Xr 20 mg , I would even go back to sleep some times after I took my pill ! Lately I have been feeling tired most of the day! but the pill works great ! I also noticed the pill is not effective later in the day when I need it to work. Please help with these questions? Your the best ,thanks for the help!!!!!