Period coming earlier every month?

My period has always been irregular, so it's always been hard to know when it's coming and when it's going to end. But lately it's been coming earlier and earlier every month. For example the days in between my last few periods were: 41, 36, 21, and 15. And now it's been 10 days since my last period and I'm having signs that it's going to start soon, has anyone had this happen or is this just a normal thing?