Suggest Medication For Nasal Infection Followed By Cough

I had a sinus infection in January and my doctor recommended Advil cold and Sinus(or generic equivalent and that is what i used) and gave me amoxicillin. Now I'm having the same symptoms again. I did not go back to the doctor because my symptoms aren't as bad as before. I have the same post nasal drip issues and a cough from the drainage. Can I mix a diphenhydramine hydrochloride antihistamine with my generic version of advil cold and sinus?