What could it be ?

On the 29 I started bleeding it wasnt heavy or nothing but almost filled up 1 tampon . And lasted til the 30th . Absolutely nothing on the 1st with pink like discharge in my panties . (Picture on my wall ) then on the 2nd only blood when I wiped once that day . Thought it was my period so I used a Tampon and it had a brown color on it . And nothing since then and today is the 4th of may . Could it have been implantation? I tested with a bfn on the 2nd . Feeling nausea with slight cramping . Any idea ? can a period last for 2 days . And can implantation accur 13 dpo?