Losing hair only on top of your head points toward male pattern baldness. But such a great loss of hair along with vitamin deficiency also mean an associated telogen effluvium. you need to restore your vitamin levels along with proper therapy for both the diseases

You are suffering from hormonal changes causing Androgenetic alopecia causing hair fall. It's completely stoppable even regrowth of hair is possible with certain medications without any side effects. Treatment depends on the grade of hair loss. So, it's a must for diagnosing which grade, you are in for an effective treatment. Please  send photos of your head, by direct online consultation for accurate diagnosis and proper treatment.

hi, it seems to be male pattern balding itself bu loosing fifty percent of your hair in three months? did you change your location of stay? or use any new hair products? your option will be start activated prp therapy or a hair transplant depending on when you are planning to get married.i would suggest you consult an exprt directly as to get more clarity on theissue you are facing.thank you!