For the past two weeks I have been feeling nautious, extreme back pain, constant headaches, frequent urination, lack of a period in two months and pain in my left abdomen. I have taken five pregnancy tests and even a blood test, and everything came out negative. I have an ultrasound this Friday and I have no idea what to expect. I'm really scared because no one has any answers for me. Is it possible that I could be pregnant and my hormone levels are just so low that even a blood test couldn't tell me?