I can never get a set time to sleep either. If I go to bed early I can never sleep until after 2am. I'll sleep in until lunchtime unless I have to get up. I've tried getting up early but by the time night comes I'm still wide awake!
No, not any new medicine, I think it is just my body clock, the only thing it seems i was doing wrong was not skipping naps.
If you have just gotten your body clock all out of whack, google sleep hygiene for ways to help yourself get back on schedule. The best thing for me when I was in that situation was getting up early and giving up naps no matter how little I slept the night before. By the 3rd evening, I was waiting for it to be late enough to go to bed.
I don't know how long this has been going on for you, but if sleep hygiene efforts don't work, some report a small dose of melatonin makes them drowsy.
However, if you happen to have an underlying sleep disorder, sleep hygiene and pills are not what you need. Two common sleep disrupters are sleep apnea and limb movements. Also, is there any chance you've started a new medicine or supplement that could be affecting your sleep?