There are a number of ways your therapist can diagnose any psychological problem that you may have.
There is a large, diagnostic "bible" called the DSM-5. Its full title is The Diagnostic and Statistical Manual of the American Psychiatric Association, 5th edition.
Yes. But, being normal is probably not what you think it is. "Normal", from a psychologist's point of view, is not 2.4 children, a dog, two cars and a white picket fence. Normal is not about where you live, your paycheck, your job or whether you get eight hours of sleep a night.