Okay me and my partner had sex a week ago my period came on it was very light and lasted 3days could I be pregnant

Since you had sex, of course you "could be" and a light period is often one sign, but it can also be so many other things also. It is too early now to test, so you will just need to wait, easiest is to wait till next month to see if you miss that period or not. If you can't wait, you can try in about 2 to 3 weeks to do a pregnancy test

Could you be? Yes. You had sex. Any time you have sex pregnancy is possible.

At this point it's too early to tell. The fact that you had a period would suggest that you're not.

Wait until your next period. If you miss it, try a pregnancy test.