Suggest Methods To Make The Periods Start Sooner

hi, i am 14 nearly 15 and i havnt started my periods, it makes me feel self concious over my body and my boyfreind asks me why i dont wear low cut tops and i dont want to tell him because it is embarrasing. my mum started at the age of 16 and i dont want to start then!! is there any medication my local pharmacy can give me to make my periods start sooner. thakyou