I am glad to hear that your therapist is skilled. That is of utmost importance. But i'm still worried about the constant swelling you are having. Does your therapist ice your knee before every therapy? My therapist did it that way and I have never ever had swelling. Maybe here and there some minor swelling, but generally taken nothing.
Your doctor does not seem to be concerned. Maybe he is right. After all he is the doctor. Would you be interested in seeing another doctor and getting a 2nd opinion? You don't have to tell your doctor about it, but it would be good to hear what somebody else has to say. That's what I would recommend. Maybe I am exaggerating. But that's better than having problems.
Make sure to rest your knee and leg. When you lie down, put a pillow or something under your leg and rest your knee that way for a while.
Are your exercises too difficult for you? Under all the pressure of exercising, it is possible that water (or some fluid, I don't know the right medical term) gathers in the knee. Talk to your therapist. Maybe changing the exercises will do the trick. We are all different after all.
When there is a knee injury, a certain cyst appears in the knee. It's called baker's cyst. And it causes the swelling/the fluid to accumulate. There are doctors who would remove it but I think that my doctor is right when he says that that cyst is not the cause of a knee injury, it's actually the consequence. So when the knee problem is solved, the cyst disappears. And that's how it was with my knee. So think about it a little bit.
Was your doctor satisfied with how he performed the surgery?