What Causes Brownish Vaginal Spotting After Missed Dose Of Contraceptive Pill?

Hi, I am on the pill, had my last period on 21st October and started back on the pill on 26th October, on Saturday 5th of November I had sex with my husband and never took my pill, on Wednesday, 10th November I forgot to take the pill again, since last friday, 12th November I have been getting spotting, brown in colour, is this an implantation bleed or breakthrough bleeding, I really need to know, I have three children already, 4,2 and 9 months