I don't know what is it and it has ruined my life

I am a 17-year-old male high school student, and I want to give some background first. I have always been very good at academics. I could understand concepts extremely quickly and memorize things after reading them only once or twice. My life was going really well until 8th grade. I was confident, good at public speaking, and enjoyed giving speeches and participating in debates. Then, seemingly out of nowhere, my life turned upside down because of one thing: OCD. My OCD became extremely severe. Living normally for even a few seconds became difficult. I was constantly dealing with intrusive thoughts and fighting battles inside my own head. I would spend hours performing compulsions. I remember days when I didn't sleep at all because I was occupied with compulsions throughout the night. Some of my compulsions were also extremely embarrassing. Sometimes, I would repeat certain words verbally over and over again. Don't even get me started on academics. I became almost completely unable to study. I started failing my classes, and at one point, I didn't go to school for an entire year. I spent hours crying alone in my room. I stopped meeting my friends because I was afraid they would think I was crazy. I went to a psychiatrist and a therapist, but unfortunately, I didn't get much better for almost two years. Eventually, though, things slowly started improving. Most of my compulsions are now gone, and in many ways, I am doing much better than I was before. But one extremely frustrating and debilitating problem just won't go away. It is very difficult to explain. It feels like my own mind is working against me, and I don't mean that metaphorically. I mean it literally. Whenever I try to do something mentally demanding, my brain seems to stop me from doing it. The biggest way this affects me is academically. I am almost completely unable to study effectively. For example, when I try to memorize something, my brain constantly throws random thoughts and interruptions at me. These thoughts don't necessarily have any meaning. They feel more like interruptions that prevent me from maintaining my focus. Even while writing this paragraph, whenever I try to think of a particular word, my mind sometimes blocks me. Because of this, I struggle to recall information, memorize things, formulate thoughts, and put them into words. I can study for hours and genuinely put in a huge amount of effort, but when I try to recall what I studied, these interruptions interfere so much that I feel like everything has disappeared. And this isn't limited to studying. It affects almost every cognitive function I rely on. Reading, speaking, brainstorming, recalling information, forming thoughts, and trying to express myself can all become extremely difficult because of this problem. The frustrating part is that I still have control over my physical activities. So I try to do everything I can physically control. Even when I feel incapable of memorizing or studying properly, I still sit down and try. I work out every day, eat healthy, and continue pushing myself. The heartbreaking part is that nobody seems to understand what I am going through. People sometimes label me as stupid or incapable, and it hurts because I know that I wasn't always like this. I know what I was capable of before. I remember being the person who could understand things quickly, memorize easily, speak confidently, and perform well academically. Now I constantly watch other students move forward while I feel like I am fighting just to stay in the same place. A normal student can study harder and improve their grades, but for me, it feels like no matter how hard I study, something inside my own mind keeps forcing me backward. I am putting in the effort, but I don't feel like I have control over the thing that is preventing me from benefiting from that effort. I had always dreamed of getting into a prestigious university. Now, sometimes, I feel like that future has been taken away from me. All of these problems seem connected to this one particular issue, whatever it actually is. Because of it, my confidence has completely fallen apart. My perception of myself has changed. I constantly blame myself and often feel like I am the worst person on the planet, even though a part of me knows that I am genuinely trying my best. I just want to understand what is happening to me. What could this actually be? Why does my mind seem to interfere with almost every cognitive task I try to perform? And why has this remained even after most of my OCD compulsions have improved? I have seen both a psychiatrist and a therapist, but so far, neither has been able to explain what is happening or make this particular problem significantly less intense. I desperately want to understand it because it is affecting almost every part of my life, especially my education and my ability to see a future for myself.