How can I boost my concentration?

I have a big exam just in 84 days, I'm not ready yet, I can't concentrate on my lessons and I just lost my hope because it is the second year I'm trying for it. I can't even sleep right! I sleep like 6-7 hours from 3:30-4 A.M. to 11:30.
What am I doing instead? Good question! Walking and daydreaming, mostly + switching between 3 apps, on occasion :|