I feel the exact same and I have tonnes of revision and work to go through also!
I normally go to sleep at around 10:30 and wake up at 7 (sometimes 5:45) on the day of an exam, but I still feel extremely tired and these past few days have been extremely bad for me in terms of sleep quality/time..
It might be an option to see your GP and ask for a blood test, as a deficiency in iron or vitamin D can lead to tiredness, which is what I've had, so I'm having another blood-test soon.