My last period was the 13th of august i have had unprotected ual since then with my fiance.?

i have now started my period on the 10th september & for 3 days it was just breakthrough bleeding not enough to were a panty liner & now on the 4th day it is light and pinky red but still not enough to were a panty liner & it is only visible when I go for a wee & wipe myself. I have done a pregancy test and that was negative. Have I done the test to early do you think I could be pregnant?