I know every female is different, and there bodies all react to it in different ways, but how earlier is it possible for these symptoms to start appearing after you've had sex.
Typically, about 2 months. Try to separate the sex episode from the pregnancy issue in your mind and you won't have preg symptoms unless you really are preg.
It can take 3+ days for an egg to implant itself once its firtlized however as soon as an egg is firtilized chemicals are released that tell the body to expect implantation not that one will happen as sometimes an egg simply misses implanting. So my thought are it could even happen before she is actually pregnent in medical terms. However it is possible for some women to go full term without ever knowing it typically obese women who dont notice any real change. I would say that with sperm taking up to 12 hours to travel to the egg anything less then that would most likely be in her head.
Well, for me I was having cravings, sore breasts, and food aversions before it would show up on a pregnancy test. I would say for me it took about two weeks.