I took a good 10wks to get my AF back after Alister and he was only BF for a few days (milk never came in) and even now they are still all over the place.

Its possible, but also just as impossible that you're pg kwim? Sometimes it is so hard to know for sure once we've had a bub what AF is going to be like - in my case it was heavy and longer, but it isn't like that for every woman either. If could have been AF and only been short and light because you are BF. If you are worried, do a test in about 3 days time I reckon.

Implantation bleeding isn't consistent with each pg either - I only had it once out of 4pgs.