irregular period

I went to the gyno last year in November (I know I need to go again just waiting on insurance) and she said everything was normal but I have a pretty irregular period. Sometimes it'll be perfect for a few months and then goes crazy again and I'll have up to 40 day cycles sometimes longer. I'm always so scared I have pcos or something but the doctor didn't say anything about it. Any other reasons I would have an irregular period?