Choose a schedule, period!

My period has been driving me CRAZY these last few months. Sometimes it's a week late (like my last period) or a whole week early (like the one that started today) when it used to be like clockwork. I have no idea what's going on anymore. I even went to the doctor and had them run a bunch of tests and had a pap smear and no sign of anything weird. Come on ovaries and uterus, we're 27, this behavior is not acceptable ugh! Any of you had this happen to you? Did it take long to go back to normal?