you probably are just stressed...i remember one month in particular I HAD been sexually active w my bf, my periods are normally irregular anyway but not that irregular...due to the TONS of stress i was under during that month(nearly had a breakdown) my period was TEN days later than expected...I was nervous as all...even though I always use protection..that was a looooong ten days...if you are worried about pregnancy just take a test to ease your mind, but I do believe stress can be a factor in some people....maybe you can look into going on birth control so it will be more regular...its definitely helped me, and actually knowing when to expect it is a nice change