My Son Has 7 Months Has Common Cold And Runny

My son has 7 months has common cold and runny nose i gave him antihistaminic and otrivin for 2 days then in 3 rd day have a fever take cefixim antibiotic then he is good now but i have a problem he has stuffy nose and blocked must take otrivin to sleep or feeding .N.B. antibiotic dose in the 3 rd dosE now.how can avoid this blocked nose