What Causes Prolonged Menstrual Cycle?

My menstrual cycle is often longer than 35 days, with an average of 38 days. I suspect I have Oligomenorrhea and am wondering how serious this is, and how worried I should be. Do most women with this condition get successfully treated? My husband and I are trying to conceive and this really worries me. I am 27 years old and am not an athlete/ rigorous exerciser.