If I were to become a psychologist...?

Psychology, some other sciences, preferably chemistry or biology, and math. Depends what type of psychologist you want to be though.

If you were studying to be a psychologist it would depend on what part of the field that you would want to get into. For instance my brother is a psychologist and also a professor. Yes, he does private practise but that's not the core of his profession. He likes teaching more than the therapy part of the practise. Where as my daughter wants to be a neuropsychologist and she will have to study not only the basics of psychology but also neurology. So while my brother had to take classes in psychology and math like statistics. My daughter will have to learn more about how the brain and the body interact and how people learn since one of the main things that neuropscyologist deal with is learning disabilites, so they have to know how others brains work. So a lot of what you learn in school depends on what you specialize in.

A general course that leads to a degree along with psychology major would be necessary, but Ph.D would be best later. Be aware that many psychological teaching in the non-Christian schools is anti-biblical and sometimes the professors put a lot of pressure on you to believe what they believe. The humanistic psychology is totally anti-God so be aware that you will be up against some spiritual warfare if you are planning on serving the Lord with the psychology.