If there is severe pain when the therapist pushes to straighten out your knee, ask him or her to back off a bit. It should be uncomfortable, not extremely painful.

I would also take pain meds an hour or so before therapy. At two weeks, overall, pain should be subsiding and you should be able to ben the knee further (flexion) and straighten the knee (extension).

Everyone is different. You may be pushing too hard on the exercises. Bend the knee as far as possible until there is some pain from resistance. Each day, you should be able to go a little further. Ideal flexion is 120 degrees or higher. Straightening the knee should be as close to zero as possible. Everyone is different of course.