Suggest Treatment For Severe Coughing At Night In Children

My 1.5 year old daughter has not been immunized. Her school sent a letter yesterday that Pertussis is going around. She has had a cough for 4 weeks, primarily at night, which many children have had, with little worry. The past two nights have been much worse, with little sleep due to coughing. We have an appt tomorrow at 2 pm to check for pertussis and to receive treatment. Any suggestions for tonight for better sleep? Cough medicine? Which kind? Mix with anything else for relief? Thank you,