Performance Grading based on years of experience

In my job, I have constantly tried to produce the best results. Over the course of 1 year in this company ABC, I have given so much from my personal time. When the time came for a performance review, I graded myself A on almost everything if not B, I recently had a chat with my manager and he said that he could not give me a A grade as I was here for 1 year. The results I have produced is visible company wide and many people have praise me for my work. But here I am, working hard but yet undermine. I don’t quite understand how this could be.

It’s really putting a toll on my mental wellbeing as I am truly affected by this. I wonder if there is anything else I could do to improve my situation or just leave the job?