If you were carb-heavy before, then there is definitely an adjustment period for your body when you go low carb. Just keep doing it and give your body time to adjust to the new way of eating. You will sleep much better once you’ve adjusted
This has been a problem for me, too. I think Dr. Jason Fung mentions it in his book- something like it’s possible that IF/OMAD triggers our brains to be more wakeful so we can go search for food
Anyway, I take melatonin (10mg) and it helps a lot. I also sometimes take Benadryl but try not to often.
End your meal with some good fat. Magnesium may help as well. Try all the sleep hygiene practices. listen to your body and try changing something - maybe you have an extra meal a couple of days a week. Maybe you add more high fiber carbs to your meal.