There are 3 possibilities that I can think of.
One is that as May4you said in posts to you on the other forum, the two drugs tend to cancel each other out and you just haven't hit a high enough dose of the adderall to have an effect. Doctors typically start patients out on the lowest dose and than gradually move up depending on the results.
Reason two is kind of like one and that is the dose is somewhat dependent on body size. So there is always some trial and error involved.
Reason three is that you also have something like ADHD (which could be causing part of your anxiety). If this is true than adderall will affect you completely differently than someone without ADHD.
By the way, you have been driving yourself nuts over this issue (and I can understand why). You really need to sit down and talk to your doctor and have him explain why he is doing what he is doing. What you should expect. How it affects your heart, etc.
Just for the heck of it also go here - http://www.medhelp.org/medical-information/show/2157/Attention-deficit-hyperactivity-disorder-ADHD?page=1#sec_3761
Check out the symptoms of ADHD and see if you ever remember having any of them as a child. In the book, "The ADD/ ADHD Answer book.", by Susan Ashley - she says that adults with AD/HD are 3 times more likely to experience significant stress, depression or other emotional problems. Good Luck!