I would try increasing your salt intake. Lower carbs also lowers insulin and low insulin causes you to shed fluids which can upset electrolyte balancing. If extra salt doesn't help, you might try an electrolyte drink (though they often contain gluose as well) or adding magnesium. If magnesium doesn't help with the sore muscles, then try potassium. Another supplement that can help with muscles is Co-Q10.
Most of the LCHF experts recommend people drink bone broth or bouillion while they're adapting to a low carb or ketogenic diet.