Hi I think you should do a urine pregnancy test to rule out pregnancy first. If negative, it can be due to some stress factor or hormonal imbalances also. Vitamin D deficiency can be one of the reason of delayed periods. You can take vitamin supplements. You can take some medicines like meprate or deviry for inducing periods if pregnancy test is negative. Also get a thyroid profile and prolactin level and a ultrasound done to see uterus and ovaries to rule out any other cause. Hope it helps.