What Causes Watery Discharge During Periods ,back Pain And Cramps?

I noticed last night that I have started my period about 1 1/2 weeks early and the "blood" is watery and orange. This is also accompanied by severe back pain and cramps. My dr changed the type of birth control pill that I take this month. How severe should I let the cramping get before I go to an urgent care or call my dr? And why is the blood orange?