How Can Constant Diarrhea In An Infant Be Treated?

I have a 15 week old son. We took him to the pediatrician thursday due to him having diarrhea for over a week (4-5 runny diapers a day). We thought it could be teething, but turned out there is a viral infection going around. Dr said he had to let it run his course since he was so young and they don t have anything to prescribe them that young. He also has a cough and stopped up nose with it, which dr also said that his lungs were clear, it was just in is throat. I have been doing saline drops and using the nose sucker for about a week but he is still congested. Started nebulizer treatments twice a day, but now he has gotten hoarse. Is there anything I can do to help get him to feeling normal? (He does go to daycare) I feel so bad for him. I have been holding him upright sleeping next to a humidifier and using baby vicks on chest and feet.