I have a 3 mm kidney stone. kidney function off a little bit. is this because of the kidney stone? do kidney stones cause permanent damage?

At your age, just by blood test result your kidney function "seems" still normal even when you lost one kidney three months before. So a small stone in one kidney should definitely not affect your overall kidney function. You should be evaluated by a nephrologist for the abnormal kidney function. Good luck.

A 3mmstone dose not cause kidney damage and is passes by itself over time- if not in a pocket (diverticulum). Drink a lot of water and you should pass it, Srain urine to catch stone if passed and have it analized for further management. good luck