I Am Self-treating My Chronic Dry, Nonproductive Cough With Mucinex.

I am self-treating my chronic dry, nonproductive cough with mucinex. My PCP has prescribed a codeine-based cough suppressant, which seems to take a couple of hours to quiet the cough. She has also tried me on tessalon pearls, but they have no effect. I have been battling this persistent cough for years. It seems to be allergy related. It may stop tomorrow and I'll be symptom free for several months only have it to return suddenly for no apparent reason. Are there any side effects I should be aware of with taking mucinex? I am type 2 diabetic, mildly hypertensive (on norvasc), and take lipitor for cholesterol/
I await your response and appreciate your timely input to my inquiry.
Lila Shafer