I'm sorry, I think I might be misunderstanding what you mean about your cycle? You have your period for 13 days? Do you mean you bleed that long? Sorry..had never heard of that and am curious.
As for when to take a pregnancy test, tamtam is correct. The best time is the first day of your missed period. However some brands such as First Response and ClearBlue say you can take them up to 5 days early. Good luck to you!
Wait for your period to come and if id doesnt then take one. if it shows neg it may be to early so try within a week or so good luck