Suggest Medicine To Increase Hair Volume

hai..i m 19 years old girl.in my family all girls born with thick hair ,,and same goes to me.But when i am in 18 years old my hair started to drop n by time flies my centre of hair started to loose a lots of hair,,especiali my centre head hair..sum say it is because sun exposure..what should i do and what kind of vitamin should i consume.i want back my thick hair please..help me... :)