Vivi,
If your temp dips within 2-3 days after ovulation, it could be fallback rise. Some ladies will see that on their bbt chart. I have that too. Fallback rise is a BBT chart pattern in which your temperature rises after ovulation but then falls back down immediately. This usually happens at 2-3 dpo. It then goes back up shortly after.
Before O, estrogen levels peak and then drop, causing LH level to peak and then drop, causing ovulation. One theory of fallback rise is that the estrogen level is still dropping after the LH level has dropped, and the progesterone levels have not risen high enough to push the temperatre up. Estrogen causes low temps, progesterone high temps. By the next day, the estrogen level is down and the progesterone level pushes the temperature back up.