Talk to Gynecologist on Long Periods Some Time

I have a bad problem with my periods that some time most often after 3 4 month cycle of regular periods, some times they come after 11 days or a week and lasts for upto 13 to 14 days, with gradual increase or decrease of bleeding.I also experience burning sensation in my pubic region and cramps in my belly.. kindly suggest me what to do, is it some serious medical hazard ?????I am much worried about it