I've convinced myself that I'm a bad student and I can't do anything right, which has led to my self-esteem being very low. What can I do?

Unfortunately, this unique quality of low esteem exist in human only, God or whoever you think had created this universe has not put this function of low esteem by default in any of his creation, a small tree doesn't feel inferior against huge trees, a small cat doesn't think it's small, the river flows at its own without comparing itself with oceans, everything has it's own harmony and is unique. You too must be having a unique quality other than studies which would be beyond the success of studies, the comparison is the cause estimation, stop comparing, you will Excel.