Sounds like your pregnant ,,,,,,,
It is pausible no birth contol is 100%. I did not notice implantation bleeding. I had a short periodbut my ultrasounds shw I got preg after. SoI didnotice some spotting but nothing serious..goodluck a test should tell you.
It is possible that you are pregnant. Have you taken a pregnancy test? It could be something else too though. Do you have an OB for paps and such? The black out concerns me. You may want to make an appointment to see your doctor just to be on the safe side.