Hi Thank you for asking HCM I have gone through your query. You shouldn t take antibiotics with out any prescription from a doctor. It can do more harm than good. Bloating you have is most likely due to dysbacteriosis after antibiotic therapy. For sinusitis not always antibiotics is needed. Nasal decongesants like phenylephrine or local decongesants like oxymetazoline, NSAID like nimusulide and antihistamine like cetirizine will be helpful. But in case of moderate to severe infection antibiotics can be used judiciously according to need. Omnicef is cefdinir which is quite strong antibiotic. If there is no improvement even after decongesants and antibiotics then x ray of paranasal sinus should be done and puncture and drainage of sinus will be needed in some case. Hope this may help you. Let me know if anything not clear. Thanks.