Why is my crown just now hurting? I got a new night guard about 8 months ago. Is this related?

I would take the guard to the dentist and have them adjust it in the area of the front teeth. Sometimes a night guard will fit so tightly, it will cause discomfort in some of the teeth.

I find that sometimes night guards can be tight on the front teeth, and I often have to relieve this area on the night guard either before delivering them, or as an adjustment later on if the patient complains of this symptom. I would go back to your dentist and explain what the issue is, and see if he thinks the night guard needs adjustment. Hope this helps!