Yup all good advice above.
The deal is its largely hormonal.Heavy resistance training releaseing is it epenephrine and endorphines, dopamine. adrenaline etc. basiclly gets you HYPED the hell up ( why I like AM workouts)
and cardio does the opposite, well long low intensity cardio. releases seratonin and can help you relax and get ready for sleep.
excuse the sp above.
Try the complex carbs and some melatonin I hate that ambien crap just doesnt feel good but knocks you the hell out.