Late & light period

Hello all! Me and my SO began ttc last month, I got an lh surge on day 19 and we BD a few days before and after the surge. My period was late this month, I'm usually very regular with my period coming on day 35 or 36. I began spotting on day 38, then on day 41 I began bleeding. At first I thought it was AF, but it's very light and keeps getting lighter. I'm currently on day 43 and my tampon wasn't even full when I took it out. I did test on the day of my missed period and got a bfn. I'm waiting until bleeding stops to test again. Is this just an abnormal period or is there still a possibility that I'm pregnant?