Can I Take Cifran For Sinusitis Problem But What Is The Dosage?

HI,my name is Vesna and my query is that i was ill for more than three weeks,in beginning i was taking tablets for cold and flu,i have permanent headache, blocked nose,sore throat all symptom usually for cold after 10 days taking tablets for cold and flu my health was even worse i has strong headache i was thinking is sinusitis problem and I have only CIFRAN 500 from antibiotic i try to get appointment to my GP but they give mi after 3 weeks so start taking CIFRAN and am not sure how to take and after taking one of tablet CIFRAN i have blunt pain in the lower part of the stomach and last think is I'm trying to get pregnant in the same time :( ...Many Thanks for your time.