1. Unhealthy lifestyle 2. Genetic tendency 3. Hereditary tendency 4. Telogen effluvium 5. Cicatricial alopecia ...etc all these can be possible reasons. My suggestion is that you visit an allopathic dermatologist near you personally to get yourself diagnosed . Solution will depend on the diagnosis. Treatment takes time so remember that you will need to be a little patient . Hair regrowth will again depend on how severe the baldness is.
Do read this article http://www.skinmatra.com/single-post/2016/09/17/Listen-to-your-skin-talk-Here-is-how
Also before you choose your dermatologist read this too http://www.skinmatra.com/single-post/2016/07/03/Skin-Troubles-Here-is-WHAT-NOT-TO-DO