I can’t really explain what’s happening either, but first of all, I do not think you should assume any symptom is going to get progressively worse until you can’t walk. I know that’s a possibility we all have to live with, but I don’t think you can go through life always expecting the worst. A pain is just a pain, and not a reliable predictor of whether you will lose mobility. In fact, the shifting nature of it to me suggests not. If it was some kind of progressive damage, then how would it get better in one place, but move somewhere else?
If your leg is weak, it’s possible this is throwing your gait out of kilter, and causing secondary problems of musculo-skeletal pain. Muscles and joints are probably having to work in ways they normally wouldn’t, to compensate for the weak leg. So they may be getting tired, they may be getting injured. Are you having any physio to try to strengthen the leg? And does the pain respond at all to ordinary over-the-counter painkillers, such as paracetamol or ibuprofen? If it does, then you are probably dealing with musculo-skeletal pain caused by the extra effort of walking with a gammy leg.