A lot of what you're describing could most definitely be part of GAD, especially the constant worry and fearing for the worst.
Many people with mood disorders such as BP experience high levels of anxiety as a symptom of their changes in mood (and of course,some people with mood disorders also have full comorbid anxiety disorders like GAD). Remember, though, that extreme anxiety and the behaviors/subjective experiences that result from it can often mimic symptoms of other illnesses (for example, racing thoughts at night caused by worry instead of mania; heart palpitations caused by panic rather than heart problems, etc.), and it comes down to what the underlying cause is (mood vs. anxiety, for example).
Obviously, you know yourself better than anyone, but you should also take your doctors' opinions into account. Try to do some more personal research into both bipolar disorder and anxiety disorders, and really think about whether or not what you're experiencing is coming predominantly from changes in mood or changes in anxiety levels. Also remember that while many people might transiently experience some of the symptoms of BP disorder at some point in their lives (ex: changes in sleep, faster thoughts and speech, high self esteem, or depression, low motivation), the symptoms need to occur at the same time as an episode and cause significant distress/problems. For many people, these "symptoms" are just reactions to normal life events and situations. In the end, if you are still worried that what you're experiencing is indeed mood related, then you can always bring it up again with your doctor and explain it, or you can even seek a third opinion. This forum has a small list of helpful websites:
http://www.medhelp.org/health_pages/Mental-Health/Useful-Bipolar--Depression-Webisites/show/523?cid=105
Good luck!
Since your self-test are negative, I think you are possibly not only suffering from generalized anxiety disorder, but also obsessive-compulsive disorder. I say this, because it seems that you are on the edge of obsessing about your possibly having bp. I honestly do not think you have bp. It is your anxiety disorder that is making you think this way.