What Causes Missing Periods?

hello mam i am 27 year old girl...my periods are delayed by 14 days this month...i cant be pregnant as am still virgin..last months my periods were 8 days earlier but this time its late and am having pain in lower abdomen since 8 days and vaginal burning since today morning also...and am feeling pms also..so please tell me what can i do to induce my periods.