No, you are not pregnant. For everybody there bodies function differently. But if you have doubts take the day after pill if you didn't protect yourself.
You shouldn't really be getting any "brown discharge" after sex.
Many pregnant women experience spotting after sex due to the fact that the general vagina area is extremely soft and sensitive and...
If you are positive you are pregnant, then the pink can be caused by the sex act itself. The insides of a woman are more sensitive during pregnancy and can lightly bleed (don't freak out) after sex....