for the past 4 days i have been bleeding brownish blood, it has never happened to me and my periods are always regular, when i started it was the regular time for me to start, but what came out of me was not regular, i am really worried i am not pregnant i know that for sure. What could be the reason why i am having this brown discharge/brown blood coming instead of my regular cycle?

From this post I assume that you are young and just fairly recently started having your periods. I had the same problems off and on when I first began 30 years ago. I believe that it is normal. This happen to me several times..so don't be alarmed.