Feeling so dumb in second year

I guess this is just a frustrated rant. So I've never had issues with studying, remembering information, and doing well on exams. Until now. My first year of vet school was hard, but I managed to perform decently in my classes and finished the year with A's and a couple high B's. I am in my first semester of second year, and I'm feeling like I can't learn anything anymore. I study diligently every day to keep up with the material as we are learning it, then study hard for days leading up to each exam and I feel prepared. But when I take the actual exam and go through the questions, I feel so dumb like I don't know anything, and I make stupid mistakes and put wrong answers for questions I really should know. I usually remember the correct answers for all the questions I struggled with soon after I have finished the exam. I feel so dumb making stupid mistakes when I try so hard studying and keeping up with the material. I have been making all C's on exams and just a few low B's. I don't know what else to do to improve. When I go review my exams after taking them, I see again just how many stupid mistakes I made when I knew the answer (I can say the correct answer without looking up any of the information when I go review the completed exams). I'm just so frustrated with myself. I also make sure to take breaks when studying, spend time outside, and I keep up a hobby outside of vet med that I enjoy. So I don't know what I'm doing wrong to keep performing so poorly.