I'm 20, is it possible to stop hair loss and regrow my lost hairs ? Which treatment do you recommend for excessive hair loss?

Based on what you have described, it is very likely that your
hair loss is due to genetics. It is always a good idea to seek medical forms
treatment as soon as possible. This can help limit the extent of baldness. For example, you may want to talk to a hair
restoration specialist about using Minoxidil (over the counter) or Finasteride
(available as a prescription). Minoxidil increases blood supply to the
follicles. And Finasteride helps block the breakdown of testosterone to DHT
which miniaturizes the follicles.

You may also want to consider a hair restoration procedure at a
future point. Your doctor can recommend an appropriate time once the rate of
your shedding has stabilized. In the
meantime, adopt healthy lifestyle habits as this will contribute to the overall
health of your follicles. 

A multi-therapy approach is something you should consider.  Addressing the same symptom with different treatments can have an exponential effect.  Combining Minoxidil, Rogaine, Laser and Cellular Therapy is not out of the question for someone thinning as your as you are.