Hello Doctor, I Have Sinus Issue, Per My Physician Is

Hello Doctor, I have sinus issue, per my physician is just an allergy. I am stuffed, congested most of the time and my drainage is not working properly. I can feel saliva goes down my throat and cause coughing and I had to spit it out, from yellow to white that comes out of the throat. what is the best OTC medicine to treat that.

Thank you