What Causes Headaches And Tingling In Calves While On Gabapentin?

I am on gabapentin for a nerve in my neck which causes unbelievable headaches. Now I am experiencing tingling in the calves of my legs. My hands and arms will go to sleep for reasons I do not understand. Very cold hands and feet - usually in the evening. Hot flashes. I am walking, and going to the gym to try and keep my circulation and muscles in good shape.