It doesnt sound like you are pregnant. A few things spring to mind- its possible you have something like PCOS. A doctor will be able to get to the bottom of it. Good luck
If your not pregnant,and your period is late.you may well have problems ovulating as without this you wont have a period.this is so common,and likely a hormone imbalance,which a doctor can treat.try not to worry to much.as you say with irregular cycles then predicting periods is difficult.so you do need to speak with your doctor.