I'd say that you need to do a test, a lot of your symptoms do sound like early pregnancy symptoms, do you usually get sore breasts before your period? if not then this is a big pregnancy sign, a lot of women notice that.
The pink fluid could be implantation blood, yes.
If you do a test and it is negative, I would recommend you go to a sexual health clinic to get checked over, any pain and bleeding from the vagina after sex needs investigating, especially if its happening a lot.
Good luck
If you are pregnant the light pink color could have been slight bleeding due to your cervix getting irritated from sex. This is not uncommon during early pregnancy.