Too much sleep

Patient: My problem is i do sleep alot, i dont sleep unexpectidely but once i am asleep i will probably not wake up before 9-12 hoursi am 22 female a little bit over weight, i exercice about two times a week and i watch my eatingi have noticed that if i sleep in the am(7 or 8 am or even any time during the day) i can wake up within 6 to 7 hours with more energy than if i slept at night. when i sleep at night it will take me those 9-12 hoursplease i need to know how normal or unnormal this is and wht can i do.i was nt always like this years ago i used to sleep only 4 to 5 hours but i nap during the day and it was perfect for my school now i cant nap.