what could it be?

i’m due for my period in about 5 days and i’ve had on and off spotting (that only lasts a day at a time and it’s happened on 3 separate occasions since 2 weeks after my last period which was on the 8th of september). spotting is very very light (pinkish) and only when i pee and wipe and then it’s gone. i was concerned and took a blood test at the ER so i can rule out any infections or pregnancy and the blood test can out negative but that was also 5 days ago (10 days before my period is due) so i’m thinking there could still be a chance i’m pregnant?? what could it be? I have an appointment with my OB tomorrow but i’m just curious to hear what you guys think it could be?? HELP ME PLEASEEEE

we have been trying to conceive so if i’m pregnant we’d be soooo happy