What Causes Spotting,headache And Vomiting?

my las period were on August 20,2010, i had on Wednesday Sept 15,spotting just
one time also on Thursday and Friday,I have like spotting all day long on
Saturday and Sunday and today..i have headaches, feeling like i want to vomit
but i haven't,i was at the doctor on Saturday and i have urine infection and he
did me blood test which i don't have the results yet.He did me a pregnancy test
which it was negative.me and my husband had unprotected sex on August 28, Sept
3.Can you help what i might be please...