I have a very consistent period. 28 days last 6 days. But this month after doing ici it came two days early and only last four days. day one was weird. I spotted orange/brownish blood lightly.  (Which my normal period never does) The next day it turned into my normal period  and the third day too.  The forth day it just abruptly stopped mid day.  I've taken a pregnancy test.  Negative.   What could it be?