pregnant?

Posted by good2know

My last period was really short for me.  I started counting cycle days on the first day that I had blood.  Going from that day I am now at day 39.  I took a preg. test four days ago that came back neg.  That same night my back killed (like my normal cramping) next day the same with ab cramping too, next day just ab cramping.  Now a little bit of cramping, still no bleeding.  When should I re-test?