When I was 15 all I ever did was sleeping, sleeping, and even more sleeping. This is normal.
Now I'm 17 and I'm a night owl so it's going to bed & getting up early is unnatural for me. Still I want to prove myself and I want to be powerful. For Satan, the gods, the universe, our race (and all human races), my brothers and sisters, and my beloved ones I MUST be strong. I meditate every Morning and every night, no matter how tired I am. If I can't do it in the morning I do it in the afternoon after I arrive at home.
When I dedicated my soul it was clear to me that the road ahead won't be easy but if I keep pushing forward I'll achieve my goals.
Becoming better for my own sake and for others too motivates me.
If you really feel you can't do it take a break (1 or 2 weeks) of meditation, get as much rest as possible, relax and sleep a lot. That should help.