This is a very familiar topic with me and at my house. You can work on developing a bedtime routine to help you go to sleep.
I often take epsom salts baths to help me relax. The magnesium in the salts are natural muscle relaxers and can help your body relax along with the hot water. Exercise caution if you are diabetic.
I also would think about a project to help my mind relax. I was into woodworking several years ago. I would visualize a project, then go through each step. I would visualize selecting the board, measuring and cutting each board, then before I knew it I was asleep.
I sometimes drink coffee in the evenings to help me sleep. Often I only had to drink half of a cup before I was sleepy. I think it may have been more of the sitting still and relaxing rather than the coffee. My doctor of course pooh-pooh this and said it was the wrong thing to do. I reminded him of something called the paradox effect. Stimulants have the opposite effect on ADHD people.
If all fails, get up and do something to keep you busy. I clean my kitchen or do the laundry. I accomplish something and it helps me relax since the room is clean. A dirty kitchen is stressful to me. I also do things like sudoku puzzles or crochet to relax. I tend to hyperfocus on those projects and that helps me to turn off the outside world.
Medications to control your ADHD can contribute to your insomnia. Try taking your medication earlier in the day. Discuss with your doctor adjusting your medication to a split dose with the the higher fast acting dose in the morning and a lower dose in the afternoon. If none of the above suggestion works, ask your doctor about some medication to help you sleep.
Be sure to write and share what solution you find.
Reta