I am a graduate student in economics, and I also study economics as an undergraduate. To tell you the truth, I feel that I have never studied any economics at all, and I only know some simple economic concepts. Now it seems that these things can be found in any book of introduction to economics. So I personally think that the primary self-study of economics can be solved, because his requirements for mathematics are not very high.

But when you study economics in graduate school, you have to learn math well, because many things need math. Since you are an undergraduate majoring in mathematics, there should be no problem.

Let me give you some advice: the postgraduate exam in economics is not very difficult. It is easy to read more books on micro and macro economics. To put it bluntly, political economy means memorizing more.