Thank you for your query.
You do not mention your age or any other health problems. My initial thought is that you may be suffering from depression
regarding your work.
Also, perhaps you could benefit from help to develop your study methods.
I would suggest you visit your doctor to talk through your concerns in more detail. Your doctor may then be able to advise on any further expert help.
Does your school/college have a member of staff that you could speak to confidentially who may be able to help with study methods.
Whilst you are feeling like this then you will need to make sure you maintain a healthy diet as this will help you recover to your original good health.
I hope this has been of help to you.