Open your window in your bedroom. Make sure you have lots of blankets. You need to reduce the temperature where you sleep by several degrees below body temperature.

Then go to the bathroom and run your wrists under cold water for several minutes. Drink some cold water. Climb into bed. Close your eyes and breathe in the cool air.

Hope that helps a little. Often, we can't sleep because the ambient temperature psychosomatically "reminds" our brain that we should be up and about.