I have 3 questions that may come to help you out a lot. First, do you understand the content taught during each class and/or after each class? Second, when you go to look at the homework, do you feel overwhelmed because you don't know how to approach the problems and find homework in the other subject areas to be easier? Last, if you look into another subject area, do you find it more interesting and captivating than the ones you're currently studying?

If these behaviours are a drastic change from how you normally are, then there definitely is something at play, likely an anxiety disorder or problem. Perhaps you could control your ADHD without medications very well and the anxiety inhibits it, so your ADHD is revealed, which makes you question why it came about (this questioning would increase your anxiety) and it goes around in a circle. The other possibility is you don't have ADHD but there is an anxiety issue or a full-blown anxiety disorder. With either possibility, it's clear your coping skills aren't sufficient and it may be related to your studying methods.