Sometimes it takes several weeks to months to rehab after knee surgery, as your body has to adjust to the replacement.
Normally, intense physical therapy is needed to strengthen the joint.
If the pain continues, I would discuss this with your orthopedic surgeon, to see if a revision is indicated. Re-imaging the knee with an MRI can be discussed.
Otherwise, I would consider another surgical opinion if the symptoms continue, preferably at a major academic medical center.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin Pho, M.D.
KevinMD.com
Twitter.com/kevinmd