Can't stay asleep, work the graveyard shift.?

I work the graveyard shift as a correctional officer. I average a 13 hour day with 1 1/2 hours drive each way. By the time I get home it is after 7am. I go straight to bed but wake up at 11:30 every day. I need to wake up at 2:30pm and when I wake up I stay awake for about 30 min to an hour. I keep waking up about every 30 min until 2:30 pm. I don't want to take any medication for fear of not waking up on time. On my first day off I still only sleep until 11:30 am and find myself falling asleep during the day if I sit down and do something quiet (like read or watch a movie) I don't fall asleep while driving or anything remotely active. I also cannot be groggy or take a nap at work. Any tips or advice would be helpful.