What Causes Spotting Between Two Periods?

I have new symptoms relating to spotting between periods. excessive cramping lasting one to two weeks before my period, lower back pain starting anywhere from one week to three weeks after my last period an lasting until about two days after the start of my next one, and increased irritability. Endometriosis runs in my family and I know these are all symptoms of this but are there other things that can cause these symptoms as well.