What do i do?

I’m just in the bathroom crying right now because my grandma called me fat, I heard her tell my brother to eat eat more than me because I was getting fatter. My mom and other family members have been calling me fat too. I’m actually underweight for my age and I just don’t know what to do now. Am I just overreacting because of pms or am I not? I’m just sitting on the toilet crying my eyes out... can I have some advice?

I’m 13 years old.