Hi.. Thanks for the query.. As per your complain sinus infection can occur due to infection in the sinuses, polyps, allergies etc.. In case if you are not relieved with amoxicillin then there is a possibility that you are infected by some resistant bacteria or there is another cause of the symptoms like allergies, polyps etc.. I would therefore suggest you to simply avoid taking the medication and better you to consult an Otorhinolaryngologist and get evaluated and a thorough clinical evaluation and investigations like PNS view x ray or MRI scan can help in diagnosis and treatment can be done accordingly.. You can be advised a course of other antibiotics like Augmentin, Levofloxacin, anti-inflammatory painkiller like Ibuprofen, decongestants like Pseudoephadrine, do saline nasal irrigation, steam inhalation and use a humidifier in your room.. You can also be advised decongestant nasal sprays containing Xylometazoline or Oxymetazoline.. Avoid spicy and chilled foods.. Do warm compresses around nostrils.. In case if there is still no improvement Endoscopic Sinus surgery can be advised.. Hope this helps.. Regards.