So I Have Yet To Have My Period For This

So I have yet to have my period for this month and I took a pregnancy test on Monday that came up negative. My periods tend to be irregular but it was due on the 17th and a week prior to that I had brown/pinkish spotting. And a week after I had spotting again. What could that possibly be? And why would I have not gotten my period at all this month? I haven't been stressed or changed anything in my life style thus far