Though they each try to get your symptoms under control, they do it by different mechanisms which when taken altogether, can work even better than by itself.
So, using the table below, a patient can generally take one medication from each column at the same time (but not more than one medication contained within a column unless directed by your doctor). For example (highlighted in BOLD ), a patient can choose to take allegra, nasonex, singulair, patanase, nasalcrom, and saline flushes all at the same time.
Steroid Nasal Spray
Anti-Histamine Nasal Spray
Cromolyn Nasal Spray
Saline solutions used in nasal irrigation reduce inflammation through osmosis. Swelling is a major factor in sinus dysfunction. Removal of mucus plays an important role in sinus health, and nasal irrigation facilitates this by flushing out thickened mucus that cannot be handled by the cilia .   improving mucociliary clearance and also removing infected material.  Damage to the mucociliary transport system is an important factor in the development of sinonasal diseases, leading to a stasis of mucus.  The numerous proteins found in nasal mucus include inflammatory mediators , defensins and many whose function is not understood. 
Sinusitis can be caused by viral infections such as cold, allergies, nasal polyps, hay fever, and other abnormalities of nose and sinus cavities. Patients with sinusitis may experience bad breath, cough, fever, nasal congestion discharge of mucous, toothache, and swelling of the face. Other symptoms include nausea, headache, sore throat, and pain behind the ears. Acute sinusitis may be caused due to common cold and allergies and the symptoms may last up to 4 weeks. Chronic sinusitis results from asthma or allergies and recurrent acute sinusitis where the symptoms may last up to 3 months or longer.