I have not had a period in 3 months and am experiencing hair loss. i am otherwise a very healthy 20 year old, not overweight and not sexual active.

See your Gyn!: There are many causes of your symptoms. Examples include hypothyroidism, exercise, polycystic ovarian syndrome, dieting, pregnancy... The only way to know for sure would be to see a gyn and get some labwork. Hypothyroidism is at the top of my list because it causes both hair loss and no periods in otherwise healthy women. Best wishes!

Need some labs: It is possible that you have a thyroid or other condition causing these problems. Please see your doctor for an exam and some lab tests.