Opinions please!

Emily
 Alrighty, AF last showed up June 8th. I have not see her since then. According to go I should have ovulated June 22-27. However, in the event that it was off and I ovulated later, I possibly could have conceived July 2-3. On Sunday I had very light spotting; literally one dot and now I have nothing. I did a test on Friday and it was a BFN. Any ideas or thoughts, if I am pregnant when should I test again? Thanks in advance.