I want to become a high school math teacher. Should I get a second bachelor's degree or a master's degree?
Rather than spend months or years in a degree program, why don't you just take the ABCTE exam which if you pass, gives you a credential that allows you to teach math in 11 states. Mathematics Certification - ABCTE | American Board
Then get a job and see if you actually like teaching math, working with kids, and working in public schools, charter schools, or private schools.
If you do love teaching– you can always go back and get a Masters in math (NOT math education, but some special topic that interests you: statistics, or symbolic logic, or fractal geometry, et cetera) it will make you better math teacher and earn you a little more money. But there is no need to suffer through an expensive and often fatuous teaching credential program if you are willing to live in one of the 11 states – and if you already know enough math to pass the test that will put you ahead of many math teachers who don't really understand, or like, their subject but have a credential.