cd28 unsure on what do think.

So I am on cd28 yesterday I started to have light brown spotting it's not a normal period , it's more like discharge , Than an af ..  could this possibly be implantation bleeding this far into the cycle . ? I had positive ovulation tests the 2nd and the 3rd , so far negative pregnancy tests .  Slight cramping but not like my usual af ,any suggestions on what could be going on ? Could it be a VERY light af? Or could it be the start of pregnancy?