I think there are a lot of confounding factors. You may be suffering from low self esteem or anxiety. Or you may simply not be a good test taker.
However, if you don’t like studying for the MCAT because you hate science, then that’s cause for concern. Because at the end of the day, being a physician requires a competent understand of the workings of the human body and love of learning scientific material.
But if you simply just don’t like taking exams, I would consider doing some self-exploration as to why you feel this way.
One specific pattern I have noticed is that people struggling with their communication skills are usually those who hate exams the most. Many times they are smart people that are very good at understanding scientific concepts and applying them but have a difficult time comprehending test questions and articulately answering them. Over time, their repeatedly poor test taking experience causes them to hate exams.
If you fit into that category, I would say that you should use it as motivation to inspire yourself and to improve your reading and communication skills. Don’t let your weaknesses define who you are and what you can achieve.