Bleeding inbetween peirods

I got my period on the Jan 9th but I got a little blood Jan 21st. I have been taken ovulation test and so far have shown me I haven't ovulated. So I doubt it would be inplantation bleeding and I have never gotten this before. I have no clue what this could be. I barely noticed it unless I went to the bath room and wiped, and ovulation tests say I haven't ovualted so that is why I am doubting inplantation bleeding as everyone says thats what it is but can ovulation test be false negative?