I have knee arthritis that the surgeon would like to operate on, but that is unlikely to happen due to work commitment. I invested in a fit with Adrian Timmis not far from you. I would say it is the best money I have spent in 40++ year's of cycling. Wedges, moulded insoles and correct alingnment in all directions of the cleats has been a great help. It goes without saying the arthritis is still there, but I can cycle almost pain free.
I would say it is possible that you may also be increasing your milage so much so early.