1990 Chevy Lumina Uneven Brake Wear

I changed my brakes about a year ago, and changed the rotors on the front breaks. The left front brake pad was worn down, while the right side looked much better. After hearing some brake squeaking recentlyfor a while, I looked at the front pads, and the left side is basically gone, while the right side is like new. I do not remember for sure if I changed the calipers or not last year or not. Anyway, not sure what the problem is with it, but it is frustrating. Thanks