Af or implantation?

For the last couple of days i have been having mild cramps baring in mind i dont get cramps only on the first day of af. Af is due xmas day well i woke up this morning and there was blood on the tissue when i wiped it was light in colour and once i wiped it had gone. I have mild cramping still. I said i will wait through out the day to see if it gets stronger. I took a test yest but was neg but if i hadnt implanted it wouldnt have shown. Am i too late for it to be implantation?