Your pain that is going down the back to single/both leg(s) is called sciatica.
Sciatica is caused by compression of the sciatic nerve
or nerve roots in the lower spine. There is also inflammation around the nerves.
Very often sciatica is caused by lumbar disc herniation. Herniated disc
puts pressure on sciatic nerve. Next second common cause is spinal stenosis
(narrowing of the space inside the spinal column puts pressure on nerves going out of spine canal).
You need to consult an experienced physician, preferably neurologist
or orthopedician for physical examination and imaging (MRI). He will confirm the diagnosis and will find the cause of sciatica.
If the pain is mild, paracetamol
, ibuprofen or other analgesics will relieve your pain. If the pain is severe you need strong medications. Corticosteroid injections into spinal fluids around the affected area will decrease inflammation and decrease the pain.
There are certain Back exercises and which should be started only after consulting you physician.
If these measures fail, you can go for epidural injection (Injection of corticosteroid and local anesthetics). Ultimate step if all of the above conservative measures fail is surgery.