allforthegirl - read about your symptoms on another thread earlier today and never had time to reply, so thought i'd respond here
As far as I am led to believe (and does sound logical and scientifically plausible) - As soon as egg is fertilised; even before implantation then hormones are increased (progesterone mainly but oestrogen too) to thicken uterine walls, provide best environment for housing new baby etc, so therefore it does sound that yes you could have symptoms before implantation. And CM changes are down to hormones too
Unfortunately these hormones are present post ovulation in not pregnant ppl too, that is why symptoms can be so similar - Id think though if it is totally away from the norm for you then that could mean hormone levels are greater than usual.
xxx