Struggle to sleep

I average about 3 hours sleep a night. The main blockage appears to be my inability to switch off.  Tried: listening to music, watching telly, doing nothing for a couple of hours before bed, tried doing loads of exercise, I have been prescribed amitriptrline by the GP 2 years ago, nothing it has helped me at all.

Does anybody else struggle this way and does anybody have any ideas to help.