I Am A 20 Year Old Female And Have Been

I am a 20 year old female and have been experiencing significant hair loss over several months. Every time I brush it, wash it, run my fingers through it, lots of it comes out. I'm so scared I'm going to lose all of my hair. I am 78lbs so I am underweight and up until a few months ago was having severe stomach problems and couldn't eat. I was also under a lot of stress and was barely sleeping. Is my hair going to come back? Also. Almost all of the hairs have white bulbs at the end. Is this good or bad?