Perhaps, you read too much from textbooks only and probably you need change your studying techniques.
Black-and-black textbooks are deficient, while demonstrations with colourful engaging illustrations and animation can enable you to assimilate learning - quickly.
Here are my studying techniques below, though you might think very little of them. Feel free to delete this question, as I am respectful of criticism.
I read something from textbooks and later research into that by typing keywords in Youtube, Quora, Twitter, Facebook groups, Pinterest, Google Image, etc. Therein, I find plentiful sources for rich brainpicking and so I take screenshots of their works (maths & physics), all for study purpose only. Truthfully, I've taken thousands of screenshots and made digital scrapbooks of them, all pages enclosed with links to sources and attached with my summaries. I use Google Slides for scrapbooking screenshots.
For rich brain-picking, I follow nerds around on the internet, be they professors, engineers, scientists, etc, the likes of Richard Feynman who has daily posts in Twitter. I read their posts and view their showcased works. From professors in Twitter, I learned about Desmos and GeoGebra, the great sites where many mathematicians frequent. Wonderful calculators there, those for graphs, trigonometry, and so on. Inside Stackoverflow, I explore hubs mostly for brainpicking: namely, Mathematics, Mathematica, MathOverflow, Physics, etc. There, I study exemplary answers to exam-like questions. I see you haven't yet joined those hubs and you should (I checked your profile).
One worthwhile place you ought to visit is Pinterest. Therein, you will find great many gems - colourful engaging pins and boards on all branches of mathematics. See also those on physics or applied mathematics. At Pinterest, type in keywords like quaternions, eigenvectors, tensor calculus, etc and see what you will find. Innumerable treasures! I oftentimes find formulae for maths & physics at Pinterest.
At Pinterest, I always have boards for my myriad studies & hobbies, those on mechanical engineering, electronics, programming, etc. I collect them for myself and also for my nieces & nephews.
In Youtube, check out channels by Math Sorcerer, MajorPrep, BlackPenRedPen, 3Blue1Brown, MIT OpenCourseWare, Oxford Mathematics, Numberphile, etc. Math Sorcerer talks about conquering your fears and dealing with failure in math. He should be the first you listen to.