Should I Give Ambrolite Or Levolin For Severe Cough And Chest Congestion Unrelieved By Norvent D In A Toddler?

My son is 5 years old, is having a severe cough. I feel his chest is congested. I am giving him steam. Giving him Norvent D, twice a day 5ml. But to no relief . Which is better to give Ambrolite or Levolin ? Please help. It s water logged here. I cannot step out.