Leg/foot pain are probably my worst fibro symptoms, except maybe for ongoing headaches at times.
Heat always seems to help somewhat with these pains when they occur at night. I wear soft short socks ("footies") this time of year, and knee-high soft socks (not sure what exactly they're called) in colder months. I also try to keep a blanket or two on at night in cooler weather, but nothing too heavy or it makes things worse. Maybe try putting a microwave-heated 'bed buddy' there just before you get into bed.
Have you had your magnesium, calcium, and potassium levels checked lately?
As Sherrine said, magnesium malate does help. Maybe you could adjust your supplements/minerals with your doctor's help.
I hope they find what specifically is going on. Best wishes!! 