I second melatonin. Its always helped me when I have a reverse sleep cycle.

Whats your sleep hygiene like? Do you have a routine at bedtime? Sleepytime extra tea can be helpful.

It might suck for a few weeks but basically go to bed the same time every single night and wake up the same time every single day. Even if you dont sleep at night, it doesnt matter, you are still resting your body. Do not allow yourself to sleep during the day. Every morning if you are in a place it is possible, go out side for 10 minutes and soak up the day light. It can be tough for some people but it works.

It might be helpful to you to start practicing meditation. It may help you slow your mind at bed time. It takes a lot of practice but dont give up - it is worth it.

This method works better than any meds I ever tried, and a few years ago I tried everything.