Xl 500 symptoms and conditions

I've been taking Biaxin XL 500 mg. 2 pills together once a day for a sinus infection. Today would be day 4. The infection is improving but since I've started this drug I've been feeling totally crappy. I've had a headache and haven't been able to sleep at all for 3 nights. I lie there with pressure on my chest. The pharmacist said that is a very potent antibiotic, hard on the body but they said it's best antibiotic - but at what cost? I certainly don't want to feel like this for another 7 days. After reading all these postings I'm definitely calling my doctor to chance medications. Thanks for all the postings.