I think in TCOYF she says that the problem with using O pain to pinpoint O is that you can never tell if it is before, during or after O that is causing it. She lists different kinds, sharp- possibly the moment of the egg bursting out, cramps - possibly post o blood etc etc. She only uses it as a secondary sign.
You know what, I sometimes get sensations in that area after O, but it's not O pain. It is the corpus luteam growing. Apparently it reaches it's largest size about 7 days after o and sometimes I can feel it in my pelvis. That could be what you are feeling too?