6 days after your period started or ended?
You should always count from the day it started.
As a guide most women ovulate around day 14 (day 1 is first day of bleeding).
Sperm can live for upto 5 days inside the female body.
The egg is viable for upto 36 hours after release.
So your high fertile window is 5 days before ovulation until 2 days after.
In a typical case this is days 9-16.
You can get pregnant at any time as it is not possible to know exactly when you ovulate - some women ovulate while they are still bleeding.
If you have an average period of 5-6 days and you had sex 6 days after that, that means you had sex around day 11-12 - right in the highest fertile time.
If you use a first response pregnancy test you can take it up to 4 days before your period is due.
Any other test you can take from the day you are due.
Either way see your doctor.
If you are not pregnant you need to sort out birth control.
If you are pregnant you need to sort out pre-natal care.