This question is similar to the question posted here.
I seem to forget a lot the details I learnt before. I don't claim myself to be a math genius; rather, all the work I am able to do is only because of my sheer tenacity and hardwork -- studying all day and night for instance. I'm sure other more capable math students would do the same amount of work in a matter of a few hours, and retain it for a long time.
More specifically, one of the things I clearly lack is the ability to put material together. For instance, I was going through an introductory unit on manifolds and I came across a question that asked to prove that $O(n)$ is a manifold! I have no clue how to start integrating the information. If I were to go back to my linear algebra book, do everything (revise) again and come back, perhaps I'll be able to do this question. That's one of my main concerns: on their own, I can cover most of a textbook, but I find it very hard to flip flop between different concepts in a textbook, flip flop between different texts on the same topic and different texts on different topics.
How does one usually go about improving on this front? For instance, I have taken a course a course in point-set Topology. But if you were to ask me to prove the Finite Intersection Property, or recall the proof of thereof, on the spot, I won't be able to do this. That's why I feel like going back to my Topology book and revising it?
Could it be the case that I'm blowing up this issue out of proportion? I feel as if this problem will increase as I go on to more advanced material. It's more abstract in the first place; even if I forget some tricks in Calculus, for instance, I can always go back and recall them. This won't be that easy for more advanced material.
I find it very, very hard to retain information. Be it physics or mathematics. I go through a text 10 times in a semester for the exams; and after the exams, I am unable to recall the information at will.