I Have Pain In My Left Leg When I Am

I have pain in my left leg when I am lying down at night. The ache wakes me up after about 1 and a half hours. I walk on it several hundred steps and the pain subsides and I can go back to sleep. I have tried gabapentin. It does not help; only makes me sleepy. I have tried an injection in the back. It lasts only about 3 days. The pain occurs three or four times a night and is often accompanied by troublesome dreams. I have also tried Lyrica, which does not help. My leg seldom hurts in the daytime because I walk frequently. I want a cause and a cure, not just a pain killer. Can you help me? Local applications are not helpful either.