What Causes Continuous Light Spotting After Taking Plan B?

Hello, so i had sex and he ejaculated inside of me twice once a couple of days before and then again maybe a week later. The second time i took "Plan B" a day after and so i started to bleed around a week and half later which happened to be a week and a half before the time i should of started. It was brown and very light it would get moderately heavy from time to time but it would remain brown for the most part and red when it would get a little heavy. my period should of ended by now but i keep bleeding dark brown to where it leaves a huge stain on my underwear. is it still plan b working because i didn't bleed directly afterwards it took me a little longer to bleed after taking the pill? I dont know if i should worry or not?