Don't know if it helps but I am 18 mths post op and only now is my knee feeling a bit better. I still prefer to wear a support sleeve on my calf (it helps make the whole thing feel more normal). There was nothing unusual about my knee pre op, nothing unusual about the surgery, but it is taking ages to improve - but it has now started to happen.
Clearly a second opinion is wise, but if they take an Xray and it looks fine (which seems to happen a lot), then it could be down to you and your physio. I have found strapping a weight to be ankle and lifting my leg forward (whilst seated) and back (whilst standing), is really developing my muscles which in turn is helping my knee feel a lot better. Good luck. Carol