Force yourself to exercise for 30 minutes – no matter how wimpily you do the exercises – 3 hours before you want to sleep. Shower afterwards even if you just stand under running water.
Light exercise should relax, heavy exercise energise.
As backwards as it sounds.
As in a relaxing walk in the evening may aid getting sleep, but doing an insane gym session wouldn't, it'd wake you up. It might make you physically exhausted, but not sleepy.