Is anyone else taking QSO 500?

This is the first time I have ever felt like quitting. I am so surprised by my low grades on these assignments. I have tried to provide deeper explanations, match my work to what the rubric wants and yet I still am told I have missed so many things. My stomach hurts and I am almost scared to turn things in. I have never felt this way before. This professor is extremely strict and I keep trying to meet his standards but I just don't know if I can.