Can stress or anxiety affect the sinuses (blocked nose for over 12 months but no runny nose etc)?

Maybe. Could just be sinus, but, I've provided a visual to help you see just how many ways the major stress hormone can hurt your body. It's one reason why it is so very important to find a way to reduce stress in your life before stress reduces your life. There are many good practices for stress reduction - find one that fits you and make it a center to your daily mental hygiene. (pun intended.)