I don’t think Econ is an appropriate major for med school prep. Maybe as a minor. Look up various med school’s academic requirements for admission. You do have to have certain pre-req’s in college. You need to do some research.
I think you, like many internationals, underestimate the level or rigor in U.S. HS. While it varies, for top students, most HS offer college level math. And if they don’t kids can often get it from a local college.
(I wonder why the world thinks their education systems are so superior to the U.S., yet they still want to attend our universities?)