Irregular periods?

My periods have always been kinda irregular. I ve never been able to tell when I m ready to start. My periods used to happen around the 2nd or 3rd week of the month & then they gradually started going later in the month to where it would still be going on into the 1st week of the next month. Why am I having irregular periods like this? I m having some light cramping but no bleeding yet & it s almost the end of the month. Any info on what could be causing this would be greatly appreciated. No rude comments please!