Implantation bleeding, breakthrough bleeding or miscarriage ?

when i use to be on the pill if i didnt take it for a few days in a row...(3 or 4 days dont remember exactally) it would make me start my period, no matter how long ago my last one was! think this could be what it is? Cuz my implemation bleeding when i got pregnant was only a FEW spots of brownish blood :)