Confused! Help?

I normally have a 26 day cycle for my period, I have sex about 1 time a week if that.  Lately I have been having abdominal pain off and on.  I also have really bad lower back pain( doctor said it was a sprain in my SI joints).  I have noticed that my breasts have gotten a tad darker. My period came about 4 days early and it wasn't real heavy like normal.  It was more like a spot and for about 1 day it had a good amount. But the whole thing only lasted 3 days. Mine normally last 5.  Could I be pregnant or is it just a change in my cycle?