Hi Wattle. I sort of answered this in the TTC buddies but here goes again. I had similar spotting (heavy spotting actually) from CD19 -24 2 cycles ago. Dr said it was because I was taking vitex. I also didn't ovulate that cycle. Are you sure that you did ovulate because your temps aren't really that much higher than pre O.
If I had to guess I would say that it is your hormones causing it. Maybe from the removal of the implanon which screwed up your system. But they say you should go to the Dr if you have spotting during you cycle (that's why I went). They could run some tests to check the levels.

I hope that helps a bit sweety!