1. due to changing hormonal level and increase in androgen level in both boys and girls:one cannot change the physiology
2. You haven't provided with details of Menstrual Cycle,HB%,Thyroid Profile,USG reports
3.Improper skin care
4. your dietary habits and occupation (working outdoor?), dandruff.
5. clogged up pores may result in on and off phenomenon?
6. In Ayurveda the possible cause of acne on nose and chin is 'Shukra Dushti' i.e. Androgen problem.
7. because skin and nervous system has common embryological origin,i.e. Psycho-Cutaneous Disorder thus treatment portion also involves the mind part.
8.avoid oily,chilly,junk and spicy food,less salt in diet,saturated and trans fat
9.stay hydrated:drink lots of fresh juices and water, take high protein diet, Vitamin A
and Zinc (which reduce the production of sebum and keartin) and green tea.
10. Ayurvedic Drug 'Guggulu' has effect similarly to that off Tetracycline
11. Pranayam provide Oxygen to tissues and by practicing it you can give yourself a healthy skin.