ADD followed by IST?

[purelyfrustrated]

I'm a 22 yr old female having a hard time focusing/remembering. Was placed on Adderall for ADD. It worked great, for awhile. Then it stopped working AND the focus/memory issue got worse. Next I was admitted to the ER with heart palpitations. Diagnosis was low potassium and dehydration (caused by my IBS). 3 days later the heart issues returned. I have had an echocardiogram, holter monitor, and event monitor. End diagnosis is Inappropriate Sinus Tachycardia. I'm on a beta blocker now and have completely cut out all caffiene, cigarettes, adderall, and any other stimulant I can think of. I refuse to take the xanax my docs want me on because I don't think I have too much anxiety, it's supposed to be bad to mix with a beta blocker, and it makes my focusing/remembering issue about a 100 times worse than before.
My doctors seem to be disregarding the mental aspect of all of this... but I can't help but feel they are related. I forget my work uniform, or wear it backwards, forget to put stuff back in the fridge, forget what I was saying in the middle of saying it, forget to turn off the faucet, can't force myself to focus long enough to hear what someone else is saying. I feel like I'm slowly losing touch with reality. Sometimes it is all I can do to pay attention to the road while I'm driving!
The adderall is the only thing I have found that has even come close to helping me with this, and even if it was accurately diagnosed as ADD, the IST has forced me to stop.
What can I do?
Other details that may or may not be relevant: I get headaches 3-5 days/week that don't respond to OTC meds, I have insomnia problems that have been steadily getting worse, I am always exhausted, and I am NOT depressed (just frustrated).
I am at my wits' end! Help??!?