You can't tell until you miss your period.
There are NO reliable symptoms at six days after sex.
In fact, it can take as long as five days after sex before conception even happens. Sperm can live for up to five days inside you, so if you had not ovulated yet, you can conceive on a day you did not have sex.
Since it sounds like you didn't take plan b, your only choice now is to wait to see if your period happens.
And remember - every possible early "pregnancy" symptom can happen for other reasons, so until you actually have a positive test, any symptoms you might get mean nothing at all.