Cd 21 light bleeding?

Stacey
On cd21 of 28 day cycle I went to the toilet and there was some red/dark colour blood in my underwear. After that they has been odd bits on underwear which are red/dark brown but its mostly when I wipe and it appears pink when I wipe. This happened yesterday and today. Could it be implantation already?
​I've not long finished my fertile period