Why can I sleep no longer than 5 and a half hrs even when I take my sleeping aids !?!?!?

Hey everyone I seem to have this problem with my sleeping that has gotten a little better, but still holds me back in my recovery. I have a catastrophic brain injury that I sustained on Nov18th 2010. I realize that the sleep issues come with it, but this is driving me crazy. I go to bed around 11 and take 3 apo amitriptyline and 2 and a half melatonin. Even after all this help I'm still waking up at 5, and when I try to go back to sleep I end up doing this stupid light sleep where I think I'm awake with my eyes closed still hearing things going on outside ( my room is by a road ), but in actuality I'm asleep. This morning i look at my clock and its 6:10am so I close my eyes and open them what seemed to be maybe 20 mins later. Its now 6:45. Should I go have a sleep study done ? I've been tired for 8 months, I just wanna get to the bottom of this and I'm looking anywhere for help. minus illegal narcotics