I had sex one week before my period... I had my period but it was extremely light and was shorter than normal... could I be pregnant... is it too soon to take a pregnancy test?

Pregnancy is possible anytime you have sex. The only difference is that some times during your cycle are less likely for a pregnancy to occur.
When was your last period? Usually it is best to test after you miss a period, but you can try one a couple of weeks after you had sex as well.
If negative, wait and see what happens when the next period is due as the last one you had may have just been an off period.