5 months post op Restylane under eyes. I got sinus infection. Is it possible that the restylane is causing problems?

It is coincidental that you had some of the same symptoms after Restylane injections that you are having now.  Restylane causes swelling because HAs attract water to them. Siinus infections cause swelling and pain because of the associated inflammation and filling of the sinuses with purulent material.  The sources of the symptoms are distinct and unrelated.

The only relationship between the restylane and your sinus infection is that you are feeling pressure or swelling in the same area where restylane injected. I do not think that the infection is related to your injections. Hope you feel better soon

Restylane is a great treatment for the area under the eyes.  I do not believe that the sinus infection has anything to do with the Restylane injections.  Please consult an ENT to be examined for your sinusitis.