Pregnancy test and implantation timing

Anne

I believe I ovulated around July 10th. And then on Wednesday the 19th I had some brown spotting.....nothing heavy at all. I normally don't spot....or this is the first time I noticed it. Could it be implantation bleeding?

I took a first response digital pregnancy test today (friday the 21st) and it was negative. My period is due Tuesday. I know these tests have very high sensitivity. So I'm guessing it's pretty unlikely that I will get a positive?