I could be wrong but doesn't T3 have something to do with the thyroid and not testosterone?(tried googling it, all I got was electronics and Terminator).
As for if it's safe...probably but at nineteen years old you shouldn't need it. Your hormones should be running wild at this age and if they are any excess could cause gyno, acne, etc. (again not one-hundred percent sure).
Go to your doctor and get your test. checked first.