Thanks for the details.
The following conditions apply in your case.
Nighttime leg cramps can be caused by unopposed foot flexion while in bed, according to Medical Library. When people sleep, the muscles of their feet and calves are shortened and therefore vulnerable to nocturnal leg cramping. The cramp generally occurs in the calf and the calf muscle may visibly harden. Sometimes the cramp is caused by a voluntary contraction. You can have nighttime leg cramps in context with heavy sweating from prolonged exertion, hemodialysis or hypoglycemia. If you are taking calcium channel blockers, this can cause nocturnal leg cramps.
If you are a diabetic, you may experience leg cramps while sleeping as well as in the daytime. If you take insulin, this can lower your potassium levels, which, in turn, can provoke leg cramps. Diabetics tend to have magnesium and sodium deficiencies as well, which can cause leg cramps
If you take water pills, or diuretics like the ones you are taking Furosemide especially which is notorious for depleting potassium and incresing the sodium concentration of ones body, this can deplete your body of potassium. Diuretics help the body get rid of excess water and salt (sodium), and in so doing the kidneys put more sodium into the urine. Sodium absorbs water from the blood and this diminishes the levels of fluid in the blood vessels. This, in turn, takes some of the pressure off of the walls of the arteries, which is good for individuals with certain conditions. However, the bad part is that these pills wreak havoc on potassium levels. Low levels of potassium can cause leg cramping.
Stress, prolonged standing or keeping the knee and calves in extension or sleeping with unopposed flexion of the foot as well as peripheral arterial disease are also rare causes of night time leg cramps.
I suggest you inform your PCP about this condition and get your metabolic profile work up done, important tests should include serum calcium level, serum magnesium level, serum potassium and serum sodium as well phosphate levels.
Treatments depend on the underlying cause, mainly targetted to replace the electrolyte in low quantity in the body.
--Hope this helps--