Low carb diets can sometimes cause poor sleep, so your issues may be related. A good place to start for supplements would be Zinc - specifically Z-12 or ZMA - before you go to bed. You may also want a multi-vitamin or multi-mineral such as Biotest's Elite Pro Minerals, especially if you are limiting vegetables on your diet.
If that doesn't help with sleep, I use melatonin. Some people don't respond to it, but it helps me quite a bit.
Hope that helps.