Has anyone ever gotten a negative HPT and a negative blood pregnancy test and still been pregnant?

My LMP was 7/7/09 had sex every other day during ovulation period had very heavy sore breast 2 weeks after missed my period in august and now i am having nausea in the morning peeing alot and headaches but i went to the doctor on Wed and they did a blood test for pregnancy and it was negative and last week i did 2 HPT and they were both negative.. Has anyone had this similar experience and still been pregnant?