I sleep only 4-5 hours every day. i lay down at 12am but sometimes i don't fall asleep until 6am. i am so tired but sleep does not come what's wrong?

Most difficult: A multitude of answers & no ready known cause. Difficulty falling asleep might be ameliorated by melatonin, greater daytime exercise, setting circadian clock by routine views of sunrise & sunset, & avoidance of napping. In my medical experience the most satisfied sleep recipients have been hundreds of medicinal cannabis users; california residents in a state where cannabis is authorized.