How do I fix foggy/hazy vision 3 years after having cataract surgery?

Depends. You need to see your eye doctor, but the most common cause would be a secondary cataract which can be resolved with a simple 60 second yag laser procedure. Another cause could be late onset corneal edema which could be treated by a corneal specialist.
Depends. Treatment depends on the cause. Go see an eye doctor for further evaluation and appropriate treatment.