Don't despair too much; maths is a hard subject and even the best mathematicians struggle with new material. You're dealing with crazily abstract ideas and your

Don't despair too much; maths is a hard subject and even the best mathematicians struggle with new material. You're dealing with crazily abstract ideas and your brain just has to get used to them. That takes time. If you're having trouble with specific material (e.g. calculus), sometimes the reason might be that there's something else that you don't quite understand well enough yet that is a prerequisite. In such a case, the first step would be to identify what that is (it could be unfamiliarity with trigonometry or a lack of skills in algebraic manipulations) and then go back and refresh that.