hello there.. Oligomenorrhea is a medical term which generally refers to irregular or infrequent menstrual periods with intervals of more than 35 days - however, the duration may vary. Since you have the problem for past 3cycles , you definitely need a complete evaluation by a gynecologist with blood tests. The reasons for irregular periods can be many, some of which are as follows considering your age and history. Polycystic ovarian syndrome (polycystic ovary system) - also known as PCOS, or the Stein-Leventhal Syndrome. Many cysts (small, fluid filled sacs) develop in the ovaries. It is a condition characterized by irregular or no periods, obesity, acne, and excess hair growth. Extreme weight loss. Low body weight is a common cause of irregular or missed periods. Extreme weight gain. Obesity may sometimes cause menstrual problems. Emotional stress Eating disorders, such as anorexia or bulimia can lead to hormone imbalances, resulting in irregular or missed periods. Endurance exercises - endurance athletes, such as those that compete in marathons, may have irregular or missed periods. Thyroid disorder - irregular periods may be caused by a thyroid disorder. The thyroid gland produces hormones that affect our bodies metabolism. Endometriosis - this is a condition in which cells that are normally found inside the uterus (endometrial cells) are found growing outside it. That is, the lining of the inside of the uterus is found outside of it. Endometrial cells are the cells that shed every month during menstruation, and so endometriosis is most likely to affect women during their childbearing years. The cellular growth is not cancerous, but benign. Though there are not always symptoms, it can be painful and lead to other problems. To rule out these conditions, you should consult a gynecologist. Get your ultrasound abdomen &pelvis with blood tests which include estimation of Serum TSH,LH,FSH, Prolactin and testosterone. Treatment depends on the cause. In case all your tests are normal,To regularize menses Oral contraceptives are a good choice but in your case you want to conceive so dont go for them or if you can wait and use them for 3months , it would help you. Dont worry, all these conditions are treatable and one can conceive even after this. Coming to your second query regarding the use of folic acid, you can definitely use folic acid tablets from now. It is vitamin and has no side effects. Instead it is good to start it 3months prior to conception as it prevents miscarriage due to structural defects of baby.