Hello. My Last Period Started On September 26 And Ended

Hello. My last period started on September 26 and ended October 2. I have not had one since then. If I am calculating it correctly, I am 26 days late today. I have had some lower back pain and my stomach feels very bloated. I have also been extremely tired. i have had no spotting or discharge of any kind until today, when I started having some light brown discharge. It is not heavy and only when I wipe when I go to the restroom. I have taken 3 hpt's and they have all been negative. what are the chances of me being pregnant? if I were to actually be pregnant, why the negative tests? And if I'm not, why the missed period