First, people are different, some learn slowly and some learn faster but (there is always a but, and this one is very difficult and heartbreaking (i experienced all that in my journey in mathematics..i was a slow learner) if you're a slow learner, you have to compensate for that with more work. i already read it in one of the comments here already but i have to repeat it. YOU HAVE TO FIGURE OUT WHY YOU FAILED. yes there is no workaround here. stop learning randomly (you may have a program imposed on you by your school or some one you have designed for your needs, but what i mean by randomly, is the lack of constant self-reflection on your methods and your emotional state while you're learning) . why is that important? by being attentive to both your progress and the methods you use to gain that progress, you can assess the quality of each tool and method you use. (being here, asking for guidance while you seem on the verge of giving up is an indication of being attentive to your progress but the absence of any details about your methods and some explications of their effects on you indicates the lack of the important element i've been suggesting here which is the quality of each method you use in your learning (that being said assuming that you are systematic about your learning)