If you're hearing a pop or a click, that's probably a problem with a joint or the cartilage that cushions a joint. Maybe your hip. I'm not sure the lumbar tilt means a whole lot. We're all weird on MRIs and Xrays. Doesn't mean it's the cause of pain. Sciatica is nerve pain. It happens when something impinges on your sciatic nerve, and the pain is usually felt down the side of your leg that's affected. I've had it, don't recommend it. The two most common causes of it are lower back discs impinging on the nerve or something called periformis syndrome. That's a small muscle near your hip that in many people lies right underneath the sciatic nerve and when it gets inflamed it hits the nerve and you get the pain. That's probably what happened to me, and I got it from riding a bike a lot and hard. I'm not an expert, so obviously seeing an orthopedic surgeon and getting an MRI will maybe tell you something and maybe it won't, but again, sciatica is nerve pain and you're describing an actual impediment to movement and a popping sound which is more like a problem with other types of tissue.