Mid Cycle Bleeding

This is my 1st time having mid cycle bleeding and it wont stop until today. I started on CD16 and the amount very little, the colour red (sometimes with mucus) , brownish, and today CD21 it turn out red again. I have regular period 28 - 30 days.

Could it be implantation?

I googled it, and normally implantation occurs as early on DPO6 and only 2-3days. But mine has been 6 days. I hope you can share your experience. Thanks