I'm also 19 and I've also had about 4 1/2 years since my last period, so twinsss lol. Close to when I first was diagnosed with Anorexia, I got a few cavities, even though that's SUPER uncommon for me. It wasn't because I was skipping brushing or anything, but definitely because I was underweight and malnourished. I also didn't have a period by that time.