What Causes Pinkish Vaginal Bleeding And Backache After Taking Morning-after-pill?

Hi, i took the morning after pill 3 weeks ago but had a light pinkish, brownish bleed for less than two days, but it wasn't a flow of blood like a period , this occured about 7 days later. Could this be implantation bleeding or a side affect.. i also feel really sick, off stomach , back ache and have lost my appetite ? I just don't feel right , abit of advice would be greatly appreciated