I'm a new math student in college and so far I have done terrible in all my math classes besides one which is basically a much easier rendition of high school math competitions. I did decently well in math competitions in high school, and I genuinely do like math. However, I just don't seem to grasp college math that well. I have trouble coming up with proofs, even though a lot of them end up being quite straightforward. I make mistakes with really trivial observations, things like missing obvious cases where the mathematical object would behave differently than expected etc. Things that I really shouldn't be making mistakes on. Overall, my brain seems to just turn itself off when faced with college mathematics.
So how do I fix this? I am not sure what I am doing wrong. It seems like doing practice problems doesn't even help me that much. I also don't understand why the transition has been so bad for me even though I have done some college-level math in high school as well. Thank you in advance.