My doctor prescribed Guaifenex PSE 600 for extreme sinus congesti...

My doctor prescribed Guaifenex PSE 600 for extreme sinus congestion. I started taking the pills (1 every 12 hours) yesterday. Yesterday morning, I experienced really bad nausea & light headedness. I was able to breathe so much better, the drainage & congestion had really cleared up. I am not experiencing the dry mouth, nor sleeplessness, but I am concerned because this morning I am having chest pain. I'm a bit worried about continuing this medicine. It works soooo good, but don't think the side effects are worth it.