I would consider dropping your afternoon stimulants. Although it may be hours before you go to bed, you could be reacting to them still.
Caffeine has a half life of roughly 5-7 hours on average, though this can vary. Assume 200 mg of caffeine in your pre-workout supp at 3:30, at 10:30 pm you still have roughly 100 mg of caffeine in your blood. Your supp very well could have more caffeine than that too, or another, more powerful and longer lasting stimulant altogether. And if you hit the gym late, you are pushing it even further.
Read your ingredients for total caffeine content. Even if you respond to caffein in an "average" manner, it is probably the culprit. It sounds like you may be sensitive to it to boot though.
If I personally drink even like a diet Dr. Pepper (relatively low caffeine content) after 1:00 pm, I'm up all night, even after it should've worn off. Most likely an adrenal response or something.
Try cutting it out for a month or so and see how it works for you.
Don't sweat the workout either, that **** may help you squeeze out a couple extra reps but nothing serious, especially if you are losing sleep. Consider creatine, CoQ10 and b-complex instead. You won't feel a head rush or adrenaline surge but you'll definitely "groove" higher and experience additional energy without side effects. More of a smooth energy. And super cheap per "serving".
If you quit cold turkey, expect some sleepless nights at first while you adjust, but give it a month or so to see if you experience a difference.
Also, make sure the room is cool and dark, quiet or maybe some white noise, no TV or bright screens and all that stuff.
