What Causes Lower Back Pain, Headache And Diarrhea?

hey i been having lower back pains,head aces,diarrhea,i been cramping,and i cant even eat without feeling nausea i throw up monday then i havent had any energy i dont know if im pregnant are not i was on the birth control shot in july 2010 and massed the one in october never had a second one yet please hep me.....