My Period Has Never Been Regular.. Some Months Its A

My period has never been regular.. some months its a 30 day cycle and sometimes its 28 or 36 or even 46 days. Theres even been times where its been lighter than usual or has lasted two weeks. This has all been happening sine before I had any type of sexual encounters. Im just wondering what could be going on. Some months it comes almost regularly two months in a row and then will become irregular again. Ive heard that for periods to be late is not uncommon but it gets very worrisome now that i am having sex.