I have been going through the same exact problem for the past 4 months..I had an MRI to see if I ruptured another disc, I have had previous back surgery, the mri ruled out my disc..nothing helps this pain feel better,it is worse when I sit, it is constant, and burning in my left butt cheek, and down my thigh, and when walking it changes to the side of my left knee, and calf, and back of my thigh..the only time that I am pain free is lying down. I am so sick of this, and my DR i now thinking it could be my hip. Who knows, all I know is that I am so sick of being in pain. Oh, I also have a lot of spasms in my feet, especially at the beach. Very strange, BTW I agree, Ibuprophin does nothing, I refuse to use pain pills , but found that Naproxin helps a tiny bit. I ice all the time, nothing has changed..my next step will be going to have shots in my hip..at this point I would even have accupuncture.
Apply ice packs for the pain and inflammation and take pain killers/non steroidal anti inflammatory drugs intermittently.
If the pain does not decrease you would need to for an orthopedician and go for a knee X-ray.
Till then wear proper supportive shoes and do not exert by any intense exercises and mobility of your left leg.