How to know if I have secondary amenorrhea or primary amenorrhea?

Easy. If you have never had a menstrual period that is by definition primary amenorrhea. In that case usually a woman lacks normal ovaries. If a woman has already had normal menstrual periods for a while and then stops menstruating prematurely (before menopause) then we are dealing with secondary amenorrhea. This usually has a reversible cause that can be diagnosed with simple tests and easily treated.