On The 19th September I Had Unprotected Sex Then On

On the 19th september I had unprotected sex then on the 21st September I took the morning after pill. Then on the 25th September I had unprotected sex again but I didn't take the morning after pill. The next day I appeared to have some spotting but it wasn't like blood. On Monday 28th September I had some blood but it was light and not like my usual period. I took a pregnancy test today at the doctors and it came back negative but they said it was early to tell. My period isnt die until the 12th October 2015. If the morning after pill worked the first time is it possible I could be pregnant from the unprotected sex the second time even with this blood?