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 it is not happening, you should consider seeing a dermatologist.
Further information is in the following weblink
https://www.aad.org/public/diseases/hair-and-scalp-problems/hair-loss
Next Steps
Please get a diagnosis from a dermatologist. Treatment is simple and has different approaches. You need to discuss with a dermatologist to understand it at length.