Can you take a monteleukast with a 2nd gen antihistamine, and nasal corticosteroid? would you be able to add an additional oral decongestant like psudoephedrine to this if decongestion is a concern? is there a risk of rebound congestion?

yes/no. All of the meds cited work in different pathways to provide relief. Rebound congestion is a factor with nasal sprays that include a med that constricts the blood vessels. Over time the constriction injures the blood vessels & they leak, causing congestion. This is not a feature of oral meds like pseudoephedrine.

Depends on your nasal condition: For nasal allergy, the combination of montelukast, antihistamine, and nasal steroid should provide a good relief of nasal symptoms. In case of persistence of nasal symptoms, consulting ENT specialist is recommended to rule out other nasal pathologies, i.e., nasal polyp, vasomotor rhinitis, septal deviation.