So, I want to challenge you to start charting your cycle a little bit so you can know your body's cues and not be clueless about when your period will arrive.
The first key is to pinpoint ovulation. The Creator has kindly given us a wet veritable calender in the form of our cervical mucous. Have you ever noticed how it changes in quality over the course of your cycle? You can discern this by getting some mucous on two fingers and pulling them apart (or on some toilet paper if you prefer). Here's the pattern (starting from right after your period ends):
- Creamy (Lotiony/Milky)
- Eggwhite (stretchy, clear) *OVULATION*
- Wet (right before menstruation)
Here are some images of cervical fluid to give you a better idea (note: wet is out of order in those pictures).
So, when you have eggwhite cervical mucous, you can be sure you have ovulated. Mark it on your calender. Then when your period starts, count the exact number of days from ovulation, and that lets you know your luteal phase length! Chart this for about two months to make sure you have it right, and from then on you will be able to count off the number of days of your luteal phase as soon as you notice eggwhite mucous, and that will accurately predict when your period will start.
One more thing about cervical mucous: several hours before your period starts, you might notice a wet sensation (but no blood). Water is the first thing your uterine lining sheds, and the rest of the lining will soon follow. It used to be that when I felt the wet sensation, I went running to the bathroom thinking it was my period, only to be disappointed and confused when I saw it was not. Now I know it is the pre-shedding of water--the signal my body gives me a few hours before the real thing.
It's so exciting to know the cues our bodies give us, so we are "in the know" and not surprised. For more reading on this topic, see the book Taking Charge of Your Fertility, by Weschler.