I have pain behind my left eye and pressure behind it for 3 days. almost feels like it's being pushed out. sinuses or more serious?

Very well could: B sinus infection requiring immediate treatment. U need a CT. The only way to see all sinuses and confirm diagnosis. Other consideration, especially if not having sinus symptoms , is Migraine. Esp if nauseated. Seek medical attention if so persist v

More serious : Please seek an immediate full history and physical exam and imaging if necessary on exam by a physician. Good luck.