It is possible that you are not doing well in these subjects because you do not find them to be interesting. And for a subject to be interesting, you need to see a personal connection, I think. And in fact, everything that happens in your life is connected to history and civics. All you need to do is notice what is happening in the world around you to understand how important these subjects really are. For example, there is in the United States today campaigning going on to select two candidates for the presidency. That process is a part of civics. And that election will affect the life of everyone in the United States. It will determine whether or not we fight wars, whether we pay more or less taxes, whether various government programs such as healthcare and social security will continue, and much more. Candidates argue about Supreme Court decisions and interpretations of the Constitution. This is all a wonderful lesson in civics for you. As far as history is concerned, help yourself by bringing it to life with some personal connections. You might ask your parents and grandparents about the history they have lived through. I found this made me very interested in history. You might find out about the history of your own neighborhood or city. These are all personal connections that are interesting and that will make you feel more involved in what you are studying.
It is also possible that you are simply not putting in enough time and energy in these subjects, perhaps because you are not enjoying them. I think that part of the reason we don't put in enough time and effort is because we believe we are not good at something. But the fact is, if we put more time and energy into the things we are not good at, we get really good at them! And then we don't mind working at all. Try doing your reading in smaller doses, a few pages at a time, making notes while you read. Make up some little quizzes for yourself and test yourself. Look up any vocabulary words you do not understand and write them in sentences. Discuss the ideas you read about with someone else. Don't be discouraged if you don't improve dramatically right away. Think in baby steps. The more time and effort you put in, the more it will pay off in the long run.
History and civics are so important. There is a reason they are taught in the schools and that you should learn them, not just to get a good grade! Learn why they are important by paying attention to what is going on in the world and talking to people who can share with you the history they know about. Put some more energy into your studying, just a little at a time. You can certainly get better at this, I know.