I've got sinusitis (sinus infection) and was prescribed Guaifenex...

I've got sinusitis (sinus infection) and was prescribed Guaifenex PSE 120 TAB Ethex. Taken twice daily. So far I've had 3 doses, got to take one in a few hours soon. Every time I take it, anywhere within 15 (maybe 30) minutes - a few hours, I get severe abdominal cramping, and sometimes bloating. I thought maybe it's just that I'm not eating enough and there's air pockets in my system that's causing the cramping. But it only happens when I take the meds... Is abdominal cramping (like a bad menstrual cramp) normal??? Plus I do feel like it is harder to sleep, and at times have felt feverish, or like I'm just burning up, that the room is so hot. Anyone experiencing any "sexual" side-effects from the drug?