These requirements will vary by state. Being a psychologist requires that you have a Masters Degree. Many schools offer programs that allow you to become certified once you complete the program. The best thing to do is discuss your options with your school guidance counselor.
With different levels of education, you are qualified to do various jobs in psychology. A Ph.D is what is usually thought of as enabling one to be a "professional psychologist", and would require 4 or more years of further study beyond a bachelor's degree. With a Ph.D., one can do clinical, teaching, or research work in the field, and counsel patients having emotional/psychological difficulties. With further training, some states now allow psychologists to prescribe medications.
Depending upon your state requirements:
an MFT (Marriage/Family Therapist) degree qualifies you to take a state exam certifying you to a professional counselor or therapist (not psychologist). Normally, you will need up to 3000 hours of
intern practice prior to taking this exam and getting certified.
A Phd (dissertation) in counseling or an area of specialization in psychology along with passing other state exams, would qualify you as a professional psychologist.
You might want to look into various career options and requirements for counselors, therapists in your state, and also explore more what area of psychology or "para- psychology" appeals most to you.
It depends on what you mean by a "professional psychologist." Technically, a four-year degree. If you mean "one who can counsel," you simply need a master's degree, not a Ph.D.