There are many causes of hair fall at your age like some recent illness, hospital admission, physical or psychological stress and more commonly androgenic(male pattern baldness/hereditary). The former causes are transient, however for androgenic alopecia you need to consult a dermatologist as this is a gradualy progressive condition. They usually give minoxidil 5% lotion to be applied over the scalp twice daily along with multivitamins like adgain.