I m suffering of sinusitis after my flu its been a month already, how can I free from that?

See your dr. You should have it looked at. It maybe congestion, a persistent infection, or related to an anatomical problem. The possibilities are too numerous to narrow it down without an exam, x-rays, culture, or evaluation of your medical history.
Se specialist. The doctor you do see should be an ear, nose and throat specialist, as most internists and family physicians don't have the equipment necessary to examine you correctly. You should have this type of specialist examination.