Melissa, if your cycles are always around the same length, that means you are pretty regular(and it's a good thing). You can temp orally or vaginally, b ut you need to be consistent with whichever one you choose.
I'll give you a few examples based on my old LP:
One month everything was fine and normal, I ovulated on day 14, I had my period show up 14 days later and had a 28 day cycle.
The next month I had midterms and was stressed to hell, I didn't ovulate until CD 20, I had a 34 day cycle.
The next month I have no idea what happened, but I ovulated on day 10 and had a 24 day cycle.
My ovulation days varied and changed the length of my cycle, but my LP didn't change at all. I miss those days