month long period?

Ok so ive had really wierd periods that are impossible to track, they don't start on the same day, they don't end on the same day and, they're during different periods of the month. The only thing is they're almost always consistently a week long. However a couple of months ago I missed my period for 3 months in a row and then started bleeding out of nowhere very heavily for a month straight. It still hasnt stopped and im really confused. Im a virgin and im 17, anyone have any advice?