The hard days, such as legs and back, also traumatize your nervous system the most. I know where you are coming from because after a heavy squat session I literally feel shell shocked. In that state I can be difficult to get proper restful sleep.
Before recommending any supplements here are natural things for you to try:
- -Why do you train legs and back later in the day? Train them as early as you train your other body parts. Therefore your mind can calm down by the time you have to go to sleep.
- Go on YouTube and search for: “Sleep meditation” If I feel restless at night I lie down listening to one of those before bed and it usually helps.
- Don´t use any stimulant products before training. Those things last longer in your system than you might believe. Especially in a body as small as yours.