Sleeplessness & nightmares while on Guaifenex PSE

I am 60 years old, and currently taking one tablet first thing in the morning, with breakfast and water for the last week. I have not slept well since starting this tablet, moving restlessly, and having continual bad dreams. My doctor wants me to take two daily, and I have declined. What is in the medication that causes this? I am sensitive to caffeine, and wonder if this product contains caffeine. Can you suggest a replacement to eliminate the chest and head congestion, and allow me to get some sleep? Please advise.