I had meniscus surgery three month ago , why still my knee swelling and in pain and since two weeks ago my right knee has pain.it is getting worse.

Depends: It all depends on the type of surgery and the condition of your knee. If you have severe arthritis, then a meniscus surgery may simply have been inadequate. If you had an actual meniscus repair (not that common), then it's possible the repair failed. Also, it's important to rule out an infection. You'll need to see your surgeon for further evaluation.