I think it's always problematic to mix medications - sometimes there are no interactions, sometimes there are. It can vary by medication, but also by individual sensitivities. Sometimes allergy meds make people drowsy, other times agitated - as you noted, the stimulants can be an added problem. Mixing that with ADD/ADHD or with the prescribed meds can cause problems in some people.
Most of the people I work with who are dealing with ADD/ADHD and allergies have used non-stimulant supplements to manage both conditions. As the symptoms decrease, they've been able to get rid of the Adderal too, working with their doctors. There is a way, particularly with the new science involved over the past 15 years and with particular advances in the past two, to reduce the symptoms of auto-immune problems (which is largely what an allergy is - the body mistaking a harmless substance for something foreign or harmful, and creating this entire reaction around attacking it) as well as to reduce the dependence on (or even initial use of) stimulant ADD/ADHD meds. There's great work on gene expression and epigenetics, which is restoring your DNA's normal and natural expression, vs. the changes that occur in the genes switching on and off incorrectly, which is caused by environmental factors (stuff we breathe, stuff in our homes, stuff in our foods, and so on). Happy to chat more if you're not getting the results you need or if you continue with the non-answers on the med combination. My guess is, you won't get straight answers from the pharmacist or the physician, partly because they don't know, and partly because the reactions can vary from one individual to another. Anytime you are working with the pharmaceutical companies, you're dealing with a well-funded bureaucracy as well as the concept of acceptable risk. I'm not anti-meds - I know there are many that are vital. But they can be overprescribed, mixed ineffectively, or creating interactions and dependencies that may not be desirable.
