Implantation bleeding

So my husband and I aren't actively trying..but a few days we slipped, once the day before my fertile days, and then once while in the fertile cycle, and then again after the fertile cycle. If any has experienced implantation bleeding..what cycle day or dpo were you? I'm thinking I'm 5dpo. And I had some light spotting today, and cramping yesterday. I don't want to be too paranoid, but definitely a little worried. We have a son already, we were just waiting for December to start trying.