Having read this I think I might have a similar problem, obviously not as severe, but there was a time when I'd get raging pains in my left leg whenever sitting down, and I didn't do anything to my leg, though I've had back problems. And at the gym, whenever I workout my left leg, I get pains in my back, nothing when working out the right leg.
Though it doesn't bother at all while I'm playing ball, I can jump just as high and run as fast, but during a two-hour bus ride it's a real bitch. Luckily, it's gotten a lot better over time. But it has been over a year where I've been in discomfort because of it.