Period always a week early!!!

For some reason the last 3 months my period has been coming a week early but I guess I should be complaining to much cuz ever since I had my daughter 9 years ago I have never had a regular period and not after my son being born almost 16 months ago my period was off until 6 months ago I'm finally getting it every month and like I said a week early I was hoping this month it would cuz Friday we are going to a water park and I don't use tampons at and I'm not sure about swimming on my period.  Ugh.