Normal cycle length is 26-32 days. If the gap between 2 periods is more than 35 days then the condition is called oligomenorrhea. This condition can be due polycystic ovarian syndrome, malnutrition, eating disorder like anorexia nervoza, estrogen producing tumors, chronic illness, hormonal imbalance, thyroid and pituitary glands problems, physical and emotional stress, intense physical activity, and use of anabolic steroids. As many factors can cause your problem, so, you should visit a doctor for differential diagnosis and treatment.