Irregular periods can be nothing to worry about, or they can be very serious. Mine are caused by PCOS, which is basically my body improperly handling sugars. After three months of birth control at the beginning of the year, my cycles are 28 or 29 days. However, I now get PMS for two whole weeks, and I gain five pounds (mostly fat!) during those two weeks, and then have to bust my ass after my period ends to lose the weight, which starts to pack back on.... ONE WEEK LATER! OMG! I am at an increased risk for type 2 diabetes. I am hypoglycemic. I have insomnia. I'm grouchy. And all of this comes from the same thing that causes me to not menstruate on time.
Oh. And let's not forget the ovarian cysts.
So it could be nothing to worry about, the sort of thing which could be fixed by a little research on the net. Or it could be very dire. You know who knows? Make an appointment. In fact, make a few.