Im trying to conceive so i started taking one a day prenatal vitamins. a month into taking them i started spotting a week before my cycle. then when my cycle came it was a week late and longer. could this be because of the vitamins?

Some thoughts...: In a woman with regular periods, some causes of a late period include: excessive weight loss or weight gain, increased exercising, emotional stress, having an illness, traveling, medicines (like birth control pills), hormonal imbalances, etc… Seeing a doctor is a good idea if symptoms are persistent, recurring, or worrisome. Typical vitamins, prenatal or not, shouldn't alter one's cycle timing.