My girlfriend hasn't had her period for 3-4 months; she is 19. She suffers from dizziness. Why is this happening? Please be specific

She needs to see a doctor--we are not qualified to give medical advice. There are several reasons why this could be happening, though. She could be pregnant, even if you think you have been as careful as possible, and used birth control every time. There is a failure rate for each type of birth control method. Another reason could be if she is very thin, and exercises a lot. If a woman's body fat percentage is below a certain level, it can affect her periods. That said, she needs to get to a doctor, even if only to set her mind, and yours, at ease. If she is also a college student, she can go to the health service.