Yes, when I was in highschool and was preparing for university entrance examination but it lasted for a short time because I realized it's terrible for health, therefore, I force myself to follow a routine.
Most of people who suffer from insomnia use sleeping pills. Have you used them? I hope you haven't used much.
During the day, except a nap, don't sleep too much. The most important thing is you shouldn't stay up late day by day, and don't make your mind stressful. Because they really cause bad effects on your insomnia.
Some suggestions for you to adapt sleeping earlier habit: in the evening, before you go to bed, let's take a warm shower; after that, drink a glass of warm milk; then, read book or listen to gentle melodies till you feel asleep.