late period negative test .. PLEASE HELP

Ashlee
I was supposed to either start my period on the 8 th of September this month or the 11 th. It is now the 19 th and nothing. I took a test today after work and it was negative . I never miss my period it always comes the same time every month . I did spot around the 26-29 th of August very light and brown . At the time when my period was supposed to come I felt so sick to my stomach and my breast are still very sore. I also have heartburn but negative tests. Is there anyway I could be pregnant either 8-11 days past my period with negative test. PLEASE HELP.. My husband and I have been ttc for about 5 months now