Sudden Hair Loss at 20 Years Old and Receding Hairline? (photo)

Losing 50 to 100 hairs per day is normal, and it doesn’t sound like you’re losing much more than that. However, it is smart that you’ve made a doctor appointment. Your best bet would be to see a dermatologist, and be honest about your medical history, family history, any drug use, dietary habits, etc. Though male pattern baldness is the leading cause of thinning hair in men, several other things can contribute to hair loss, like a traumatic emotional event, severe stress, alopecia areata, malnourishment, anemia, diabetes, and more. Once a diagnosis is made, a course of treatment will follow.

getting a medical evaluation is the best first step then go from there. once your doctor has cleared you then proceed with some hair loss treatments such as finasteride or minoxidil, your physician will be able to assist you with this.

Any sign of sudden hair loss should be evaluated by a physician familiar with hair loss and hair restoration. In many cases, patients are simply noticing more hair loss than they have noticed previously, but the rate of hair loss has not changed significantly. 
It is normal for the hairline to recede somewhat over time for men as they age from their teenage years. It is also possible for other factors to contribute to hair loss, or for a medical problem to be causing hair loss. A formal evaluation with a hair restoration specialist, facial plastic surgeon, or dermatologist would be recommended. If androgenetic alopecia is diagnosed, hair transplantation may be an option in the mid-20's.
All the best,