The blood test you had done to check for pregnancy, how long ago was this? Did you go to a clinic, or to your regular doctor?
Does your GYN know that you have not had a period since July? If you have had a medical appointment with your doctor, what information were you given? (It can be common for women to have irregular cycles, even to miss a period. Depending on your age and medical history, your doctor may want to see you to rule out any medical condition). If you have not had a medical appointment with your GYN, please call to be seen.
I understand your frustration and confusion, as we were trying for the longest time to conceive, too. Every woman is different, and there are always exceptions to the rule. It is impossible for us to say definitively over internet what your situation is, but I just do now see how you could be pregnant. Your symptoms of breast tenderness and fatigue can be related to many, many things...and there can be hormonal reasons for these symptoms and the loss of menses (missed periods). Have you had your hormone levels checked?
How long have you been trying to conceive? I know that when you are actively trying, every symptoms seems like it is indicating a pregnancy...especially when they are related to hormones and your MAIN symptoms...lack of period....would be indicators of pregnancy. However, with the multiple tests AND a blood test....I just do not see how this would be possible. An ultrasound can confirm/deny a pregnancy, if you need to "see" for yourself (I am not sure if a doctor would even do this, once a blood test has confirmed that you are not pregnant). I just wanted to tell you about this as a possibility, as there are many TV shows on where women were "surprised" that they didn't know they were pregnant as they were giving birth. If you are receiving medical care on an annual basis, having lab tests done...you are not going to miss anything.
We would always tell women to "listen to your body", but the mind is also a powerful tool here. You are wanting a baby, and it is emotionally draining to go on the roller coaster month to month of wondering...I know. It is tough. Wanting something so bad where you feel the symptoms is extremely common. And, you may actually have the symptoms of tender breasts and fatigue, but again, these are indicative of any hormonal fluctuations in your body...the same fluctuations that women have throughout their cycles (pregnant or not).
Please call your doctor for a medical appointment regarding your lack of periods, and if you have already been seen..please tell us what information you were given, as well as how long you have been trying to conceive (how old are you, by the way?).