Sometimes it is the little things that set me off. I find having enough protein at school helps me stay calmer and the brain to focus better. Every 3-4 hours I have tofu or yogurt or unsalted nuts or milk or whatever. THat may not solve all the problems but it could reduce your anxiety level to a coping point.
What about talking to the professor - maybe he could help or suggest resources. What about extra credit project?
Maybe a new major is called for unless you are firmly committed to science.
What would you study if you had no required courses. Maybe that will be a hint.