if you are sure your batteries are good, and your temp taking technique is good...
they do say some women have very stable temps. it is unusual to be that stable for more than 2 or 3 days, and you do have several charts with like 5 days in a row exactly the same.
the only chart i think i saw where they were flat at ovulation- you've got that one (december 25) on override, yes? i wouldnt pick that day for o, i'd say it was 1-2 days after that. i know your cm/cp doesnt match up just right if it were
hang on a sec i wasnt done here... im having computer issues- editing now
im sorry, my computer is majorly screwing up, so i have to make this quicker than i want to, but basically, with a +opk on cd14, you would expect o on cd16. a temp can be flat for one day after o, because, while there is no way to check your basal temp once you are up and about, it could have actually dropped that day more (not really actually dropped on paper, but your actual basal temp if it were able to be measured during the day, which it isnt) and then gone up the next day to the same level, but actually be a rise. i hope that makes sense. but beyond that, it would be really unusual to have the same temp the THIRD day after o.
the only other thing that does come to mind is this- because progesterone makes your temp increase just as if you had o'd and the progesterone was coming from the corpus luteum, it is possible that you did not actually o, but the thermal shift was the result of the p4. a +opk doesnt mean you did actually o, but that you had an lh surge, so you can gear up to o and not.
anyway, i hope what im trying to say comes across here, it's a little garbled i know. good luck!
I haven't known what to say because I don't really know about flat temps, but I hope you get your temp rise soon, hon! Thinking of you and hoping that +opk was just a warm-up! 
