Can't control my thoughts and overly thinking everything

I’m a student preparing for my one of important exams of my life and lately I’ve been struggling a lot mentally. My mind keeps automatically going back to one person/thought, sometimes around 100 times in an hour. It happens even when I’m not consciously thinking about them, and sometimes I don’t even realize that I’ve stopped studying and become lost in my thoughts.

I’ve tried telling myself to stop, distracting myself, focusing on studying, and using different techniques, but it hasn’t really worked. It is affecting my concentration and taking away a lot of my study time. I know I have important exams coming up, which makes me more stressed because I want to focus but feel like I can’t control where my mind goes.

I’m also becoming frustrated with myself because I feel like I should be able to control my thoughts. I don’t necessarily want to stop caring about the person; I just want my thoughts to stop controlling my attention and interfering with my life.

I’m looking for help understanding why this is happening and learning how to manage these repetitive thoughts so I can study, sleep, pray, and function normally again.