you should first see a derm and get your bloodwork+hormonals+trichoscopy done. but if it is confirmed that it is AGA (androgenetic alopecia aka male pattern baldness) you would need finasteride to prevent its progression and minoxidil to regrow what you had lost. keep in mind that depending on your age, finasteride may not be enough and you may get prescribed dutasteride too in addition or in replacement of finasteride.