What Causes Unusual Periods And Discharges With Stomach Discomfort?

uhmm, my period is kinda wierd this month. i had one day that was a brownish color the next was heavy like a normal period and the next day it started to end and now today it is gone. i thought i was pregnant but since i had that i dont think i am anymore but today i started getting a wierd feeing in my stomach. so what just happened?