vegetarian and extremely light periods

Hi everyone! I have been a vegetarian for one year now and have noticed my periods have changed a lot. I've heard that sometimes your period becomes lighter once you switch to a vegan/vegetarian diet but mine has become way too light that I don't think is healthy. The first day of my period I usually get really bad cramps and it's pretty heavy then the next day it's medium to light and then it's barely there... Have any of you experienced extremely light periods? I used to get them so heavy for at least 2-3 days. I'm scared I'm not getting enough of something but I don't know what. Also I am 23 years old, I cut out almost all dairy and I am underweight even though I feel like I eat a lot.