implantation bleeding?

Arolynn
This month I took soy isoflavones as an attempt to shorten my 35 day cycle. I took 160 mg CD3-7. This month AF came 2 days early lasting from the 7-11. Starting CD18-21 I had some spotting, with no cramps. CD 20 I had blood work done and it came back negative. Could it be too early? Do I still have a chance since AF didn't arrive yet? Is this Implantation bleeding?