I would say that it's simply the swelling and weakness because you are only 2½ weeks out.
I'd like to ask you some questions if you don't mind, and it would be very helpful if you would answer each one individually - numbered as I have done - in as much detail as you can then I'll come back as see where you are ....
1. what are your pain levels right now?
(remember the 1-10 scale: 1 = no pain and 10 = the worst you can imagine. And don't compare this with the bone-on-bone pain you had before surgery!
)
2. what pain medications have you been prescribed, how much are you taking (in mg please) and how often?
3. how often are you icing your knee and for how long?
4. are you elevating your leg, how often and for how long?
5. What is your ROM - that's flexion (bend) and extension (straightness)
6. how swollen is your leg?
7. what is your activity level? What do you do in the way of housework, cooking, cleaning, shopping, etc., and
8. what kind of PT exercises and exercises at home are you doing? How much and how often?
This is the most crucial question so please help me by using the format I have left as an example (which means please make a list and not an essay!)
Exercises done at home: (enter number) of sessions each day
enter exercise + enter number of reps and sets
enter exercise + enter number of reps and sets
enter exercise + enter number of reps and sets
etc., etc.
At PT
enter exercise + enter number of reps and sets
enter exercise + enter number of reps and sets
enter exercise + enter number of reps and sets
etc., etc.