B..
Implantation typically happens 7-10 after ovulation. With less then 7 days being not as common.
Yes, there can be physical signs of implantationn. However, I think it would be VERY rare to experience any kind of symptom just 4 days after sex. Sometimes, when we want things, we feel what we want. (I speak from experience, and I think every woman trying to concieve goes through the same thing.)