Can I take advil cold and sinus and benadryl together before I go to bed?

First, a question. How much of each are you taking & what is your weight & height? Depending on the chemical content of the cold and sinus part of the advil, it could have a sedating effect. Unless the package says its "non sedating" it probably does. Benedryl definitely has a sedating effect, even at 25mg which is typically the dosage packaged for over-the-counter sales (for adult use). By adding the benadryl to the cold and sinus medication you will be increasing the amount of sedation you are taking. This suppresses the central nervous system. Generally this is not a good idea unless the medications & dosages are recommended/approved by a physician. I don't want to scare you. But seriously, if you take too much, you could stop breathing and/or stop your heart. Call your doctor's office and ask for their recommendation. They can compute the dosage while taking into consideration your weight & height along with any othelr medications you are taking.