Why did (or does) your dad take coumadin? Did he ever know what caused his problem? It seems more likely to be something genetic, in my unprofesional opinion. Bit of a coincidence that your dad apparently has clotting problems, and now you do too. I assume the doctors checked that out? Did they do genetics tests?
Also, if it was something like leukemia, I'd have thought you would have already seen some abnormal blood test results by now, since you've had so many tests already.
Maybe it's time to change doctors, you're obviously not getting anywhere with this one.