If you're getting a full 8 to 10 hours of sleep but still tired all the time then you could have a condition causing your body to have too little hemoglobin or not enough red blood cells, when that happens your body doesn't get enough needed oxygen so you feel tired or weak all the time.
Usually you'll have symptoms of the low hemoglobin and low red blood cells such as pale skin, shortness of breath, dizziness, or headaches.
Another cause of being tired and weak all the time is being anemic or just a plain old iron deficiency even without being anemic.
I would schedule an appointment with your doctor to get a blood test or other tests done to figure out what is causing the actual problem of being tired all the time.
If you're getting enough sleep at night then you shouldn't feel tired during the day.