Hi
Leg pain at night from my experience is often related to neural hypoxia as you rest your blood pressure drops and the nerve loses its vascularity (a similar thing is seen in CTS at night). Try walking up/down your stairs before you go to bed and see if you sleep better. This will increase the blood perfusion around your nerves in the lower leg and might reduce your night symptoms. That might explain why you were better when you were more active.
A longterm solution will be to have your back assessed by a competent physiotherapist as you might still stand in your pregnancy posture i.e lordotic with posterior sway of your upper trunk. Thus, stressing your lower back and nerve roots. Also check your SLR with adduction of the hip and inv/ev of the foot.
Just a few thoughts. Please tell me how you got on.
Steve
Hallamshire Physiotherapy