I can offer no help for the insulin part of it, but...when you say you're allergic to MSG, do you mean anaphylactic shock-or-wheezing type of allergic (IgE-mediated)? Or do you mean that it gives you headaches, heart palpitations, etc.? I ask because I'm sensitive to MSG and have a hard time taking any pills long-term because the fillers and binders they use have free glutamates. If that's the case, your headache reactions to the meds MAY (just may) have been to the free glutamic acid instead of the meds, themselves. This seems especially likely if you have problems taking most meds, in general. Have you tried having any made specially for you without those ingredients by a compounding pharmacy?
Also, have you tried a low-carb diet? If I were in your situation, I'd try a Dr. Bernstein-esque diet, which is one of the most rigid low-carb diets and seems VERY successful with most patients who do it. I recently read his Diabetes Solution and was seriously impressed; it's not the only way, but he was a pioneer and seems to have at least one approach to diabetic control down pat.