Helpp please??

So I’m 11 days late from my period after taking plan b on the March 18. I tested on Tuesday in the evening when I bought on from the dollar store and it came back negative. Now I’m have a poking left pelvic pain and it is dull for the most part but gets sharp at some point for a while. What could this be? Update: the pain has gone away and now I’m 13 days late from my period and in my supposedly next predicted fertile window. I got some brown discharge on my underwear. Should I be worried?