I had blood in my cervical mucus.

I had blood in my cervical mucus last week. It only happened once and im expecting my period todsy but it has not yet come. The blood in my cervical mucus was red.  Could i be pregnant? My boyfriend snd i had sex on the19th of september, ehich was three days afger my period. Hd didnt cum inside mr but i understand that you can get pregnnt from precum.