Suggest Remedy For Delay In Periods

hello sir....last month i had sex with my gf.....it was 5th day after her periods.....nd after sex she had bleeding from her vagina for next 5-6 days.....nd this month her period were delayed by around 12 days........is everything fine......she is 17 completed and i m 19...her height is5'5"nd weight around 48......also she has a kidney stone