Pooh/Stoney, don't just look at one or two temps. Must see the whole picture and graph.
Pooh, it's not unusual to start with low temps immediately after O and slowly rise after O, there are all types of charts around. Some people get an immediate spike after O, some slowly inch upwards......
What I am trying to say is that if after O, if overall temps still getting low BBT, could signify that Progesterone levels are low. When Progesterone levels are low it could mean also that Ovulation did not happen. That's why Stoney, FF, not sure if you O and keeps changing your O date. Unless you use OPK and had a +v OPK and indicated it on your Chart, then FF can identify and crosscheck with your BBT and pinpoint or detect the O date (then you will see that your crosshair -the RED VERITCAL LINE and HORIZONTAL LINES will turn solid and not dotted). But just by going on BBT chart alone is very hard for FF to make guesses, need to look at overall picture, CM, OPK.... and for women with fertility problems, a lot more tests & scans, medication, by doctors...etc.
As BBT after O is linked to Progesterone production. BBT only goes up if Progesterone is present, so where there is low Progesterone, BBT tends to show lower temperatures. Usually on healthy and sustainable pregnancies, Progesterone levels are on high side....
you can google more about Progesterone....Progesterone levels alone cannot be used to diagnos pregnancy...for our naked eyes, it just shows on a BBT chart as higher levels.
Here are some easy to understand links about Progesterone & Pregnancy, hope it helps:
http://www.livestrong.com/article/81879-progesterone-levels-first-trimester-pregnancy/
http://www.propertyguru.com.sg/listing/12593585/for-rent-paterson-suites
Progesterone: The follicle from which the egg was released is called the corpus luteum. It will release progesterone that helps thicken and prepare the uterine lining for implantation. The corpus luteum will produce progesterone for about 12-16 days (the luteal phase of your cycle.) When the egg is fertilized, the corpus luteum will continue to produce progesterone for the developing pregnancy until the placenta takes over around week 10. Progesterone is the hormone that helps maintain the pregnancy until birth. Sometimes, the failure of the corpus luteum to adequately support the pregnancy with progesterone can result in an early pregnancy loss. Progesterone inhibits immune responses, decreases prostaglandins, and prevents the onset of uterine contractions.
http://americanpregnancy.org/pregnancycomplications/earlyfetaldevelopment.htm