Sleep cycle problem. Be of great help!

I was accustomed to sleep in the morning from 6AM to usually 12PM because of my late night studying habits. But these days when I have joined some classes for which I have to get up at 7:30 AM everyday it has become increasingly difficult for my brain and body to function. Because usually I used to sleep during this time and I can't sleep in the night even when I switch off my phone for and try sleeping for hours, I fail. I am extremely distressed and sleep deprived and I need some sleep. Can anyone here please help me and prescribe me come mild sleeping medicine which I can take at 10 pm and sleep for 6 hours uninterrupted so that my body clock gets on track again. It would be of great help! Thank you.