Can i use milk of magnesia (magnesium hydroxide) for primer despite of i once had kidney stone problem?

Sure: This has nothing to do with kidney stones. Most stones are calcium-based and even then, the problem usually isn't so much excess calcium as insufficient water intake. I'm sorry you ended up with acne scars -- today this is 100% preventable. Truth be told, my hope is that as you approach adulthood, you have greater access to and a better relationship with a personal physician. Best wishes.