Am I underweight or not?

latley my friends and family have been pestering me about my weight. I think im perfectly fine but everyone seems to think im developing a eating disorder. The other night my grandmother was screaming at me telling me that I look sickly and that I'm too skinny. She thinks im anerexic. I am 14 years old, 5'1, and weigh 85 pounds. do you think im underweight?