For The Last Several Weeks, My Sleep Pattern Changed: Instead

For the last several weeks, my sleep pattern changed: instead of sleeping 6...8 hours, I sleep between 3...4 and do nit sen to fall asleep afterwards despite listening to "sleep music", taking melatonin, etc.
I had balloon sinoplasty on 12/05 but had hard time believing that has anything to do with the problem.
Any suggestions?