I fully empathise, it's awful knowing u need to sleep but can't
I agree with multivitamins, also make sure no caffeine after mid afternoon (I find even if I drink tea too late it can affect my sleep!)
Also trying things like chamomile tea, valerian etc (from health food shop/holland and barrett) can help a lot of people, or even Kalms or similar (they do a night one)
If I find I'm kept awake by things going through my head I get up and write down all the stuff to be done, check stuff that was to be done ready for next day, gets it out so I'm not fretting about remembering them!
If nothing works it might be worth a trip to docs to see if they can help, a few years back I was finding anxiety was keeping me awake and I was surviving on next to no sleep, they prescribed me medication to help.
I hope you get some sleep soon xx