Due To Chemo My Immune System Is Weakened. Iwas Around

Due to chemo my immune system is weakened. Iwas around a crowd at a funeral and developed chest congestion and cough. After doctor tests, it was not bacterial. After Claritin, Zyrtec, and muscinex I now have post nasal drip causing mucus, causing coughing, sneezing and throat wheezing. How can I get rid of the post nasal drip given my circumstance?