Delayed periods could be because of many causes like Significant weight gain or loss,Overexercise,Poor nutrition, anemia, hypothyroidism, Smoking,Eating disorders like anorexia nervosa,Increased stress, Polycystic ovarian syndrome. Delayed periods wit less flow is commonly because of anemia(less hemoglobin)I suggest you get your hemoglobin and tsh test done once. Have more iron rich foods like green leafy vegetables, pistachios, dates.Consult gynecologist once.