I'm having an allergy attack. I'm already prescribed Zyrtec and Singulair and still can't stop sneezing. Can I take Benadryl with these 2 meds and go to bed?

Allergy meds. Yes - there should be no reaction with the singulair and maybe a slight reaction (increased somnolence)the the zyrtec but since you are heading to bed that isn't an issue. You might want to double the dose of Zyrtec going forward as the 20 mg dose was actually better when the drug was being developed.