Should i still be having pain 4 months after bilateral knee replacement?

No, not from your: Knees. Check with your surgeon, as (s)he will know best. Some people continue to have some discomfort for up to 6 months. You might be having another cause of pain, like from the back, where a pinched nerve(s) from a disc lesion or some other pathology could be responsible for it. See you doc or a spine surgeon.

NO: Your body may reject the nickle in the prosthesis. Could need to be replaced with non reactive metal.