Circadian Rythm Disorder...

I have PD and I have been dealing with sleepless nights for well over 25 years now. I have only recently learned that this is a common condition that is linked to neurological issues (like PD). They say that when one develops a 'Circadian Rhythm Disorder' it could be an early warning sign of PD. I tried taking Melatonin many years ago but I found that it was only effective for maybe two or three nights. After that, nothing. I want to ask if others here have had any luck taking Melatonin? I have been told that you must continue to take it regularly for it to (eventually) be effective...