Ur BMI is 20 normal
Have you seen a doctor? Get lab, history, exam. Is not your weight , is how physically fit you are.
If you feel sick, weak, loosing weight, diarrhea
etc then i'll be concerned. Bmi
of 20 is normal range. Again, is how you feel. Make sure you have excercise routine that incorporate (cardio, strenght, flexibility), eat healthy
, have a positve mental attitude (pma). In time you'll gain weight (age).