Guaifenex and light headedness

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.

I'm taking 600mg 2x/day Guaifenex for fluid behind eardrum. I've been on it for about 2 weeks. I was having a lot of trouble sleeping, so I started taking the second pill at noon. I am sleeping better at nite, however I am still feeling light-headedness all day. I went off the drug for a day and still had the light-headedness. My ears feel better, but I will probably call the Dr. because I am concerned about the light-headed feeling.

I was prescribed this in conjunction with Biaxin for a sinus infection. I have more pain in my head, headaches, light headedness, nausea, and a very lathargic feeling. I also have extremely dry nasal passages. After reading the previous entries I am going to stop taking it. It can't hurt.