Hi Michelle

I'd agree with Vam44, its probably patellofemoral pain and again probably caused by quad tightness in your case. Talk to the surgeon/physio about stretching but if they say you cant for a little while and your concerned its delaying your rehab you could use some other approaches to relax the muscles such as massage/soft tissue work or some electrotherapies that will help it relax.

Either way your physio/surgeon should be able to tell you about all that.