AF or Implantation bleeding?

So I was due yesterday and yesterday afternoon I could feel slight twinges in my back so knew AF was arriving. My usual periods are really heavy especially to start with and last around 4-6 days. This morning I came on but it wasn't as heavy as usual and it was bright red almost pink rather than my usual really dark red. The weird thing is, I'm already down to really light spotting of again bright red/brown blood. Could this be implantation bleeding or just a weird period?