The hair cycle normally consists of growing, resting and falling hairs and there is a delicate balance between these stages of hair cycle. Normally hair should regrow but if its not happening, you should consider seeing a dematologist. The treatment typically consists of usage of oral medication (Finasteride) and topical lotion (Minoxidil ). The dosage and duration is decided by your dermatologist. You need to be patient with the treatment protocol as it takes months to see initial improvement. Certain dermatologists supplement biotin, hair serum and advice procedures like PRP therapy which may accelerate the rate of hair growth. PRP needs multiple sessions roughly at 6 weeks intervals. Further information is in the following weblink https://www.aad.org/public/diseases/hair-and-scalp-problems/hair-loss