Implantation bleeding at 13dpo ??

So my period isn’t due until the 30th but on the 24th I had very little bleeding which was around 13dpo. Is it possible to have implantation bleeding that late? I’m still getting a bfn as of this morning at 16dpo so I have no clue what’s going on! I had cramping and lower back aches last week too but that ended Saturday. 😫😫 any ideas? Maybe af is just coming...