I Believe I May Be Pregnant Although Home Pregnancy Tests

I believe I may be pregnant although home pregnancy tests are still showing negative. My period was supposed to start two days ago (my periods are fairly regular) and, moreso, I've had some (brown) spotting the last few days that seems far too light to be my period.

Last night I used a Tampon, unaware that I'm not supposed to use Tampons for spotting. (I was also concerned that, if the negative results were right, I could start my period.) When I pulled it out this morning, I noticed a tiny bit of red blood in addition to a tiny bit of brown and it concerned me because spotting isn't supposed to be red. In my subsequent research, I found a lot of people warning to *never* use a Tampon and now I'm scared my mistake might cause a miscarriage or infection.

I have been wearing a pad all day and there is no spotting, no bleeding...i.e. no period, so I still have strong reason to believe I'm pregnant, but I'm still worried I jeopardized it. Is the small amount of red on the Tampon early evidence of something that went wrong?

I was very hopeful that I might get a positive result in the next day or two to show my husband as a Valentine's Day surprise, but if