Hello,
 It seems that somehow you have developed an 
electrolyte imbalance. 
Blood test to confirm electrolyte imbalance can be taken.
I would insist you to take juicy fruits like citrus fruits. They contain plenty of potassium which should help in the proper functioning of the muscles and in reduction of the cramps.
 You also need to increase total fluid (water) intake and to take plenty of 
ORS (oral rehydration solution) to replenish the lost fluids and salts. 
If that does not help, hot compress should provide relief. The vicious cycle of pain and spasm needs to be broken and I would insist you to take 
Paracetamol or 
Acetaminophen two tablets together twice or thrice daily for the next 3 days. 
This should ease the problem and make it go away. If it does not help I would insist you to get an X-Ray of Lumbosacral spine (AP and lateral) done and to see a physical therapist with the reports.
 Based on the findings he would be able to demonstrate to you proper exercises that should provide relief.
Hope I have answered your query. Let me know if I can assist you further.
Take care
Regards,
Dr Ivan R. Rommstein, General Surgeon