Implantation bleeding? This many days after ?

I had 9 days ago. Last night I had some spotting, but my period never started this morning. I thought maybe it's implantation bleeding but isn't that supposed to happen 3-6 days after fertilization. What else could it be? .. (Just some more info I'm feeding my 7 month old but he sleeps 12 hours at night and eats solids, I haven't yet had a period since giving birth)