You counted 11-16 days from the first day of when your last period started right (and not from the last day of your period). Because you're fertile between 10 & 14 days counting from the first day of your last period (lmp), so it looks like you had sex during the appropriate time frame to get pregnant. The spots you're seeing is a possibility of implantation because it takes about a week for the egg to travel down the fallopian tube and a couple more days for implantation to finally occur in the uterus. Were you tired around day 23? I knew I was pregnant once I started going to bed at 7:30 pm instead of 12am for no apparent reason.

Spotting is common during the first trimester also.

Good luck.