I've always been underweight, I'm a picky eater but I have at least 2 meals and snacks every day. I've got a vitamin deficiency but I take supplements for it daily so I'm fine but around the time I was diagnosed years ago, doctors were surprised that everything was fine with my period. I've never had an issue with it I've had a period every month since I started it. A doctor told me it was a miracle I was still menstruating and that my period will stop but it hasn't years later. I think she was lying just to scare me. I doubt my period will ever stop until I'm old and get the menopause.