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

Early hair loss in patients with a strong family history of hair loss is not uncommon. After an evaluation with a hair restoration specialist to rule out other medical issues that may be causing hair loss, multiple treatment options exist for young patients with hair loss. 
Minoxidil topical is a great option and can be safely used by most patients for many years with very few side effects. Finasteride (oral pill) is a very powerful medication for slowing or stopping the progression of hair loss. Another option in young patients is PRP injections, which are performed over a series of treatments using the patient's own blood. Finally, laser/light therapy and other topical treatments are available. Hair transplant may eventually be an option, but not at age 20. I typically recommend that patients are approaching their mid-20's before considering a transplant session.
All the best,

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.