What can i use for my childs cough and congestion?

my child is 3 weeks old, has a cough and is slightly congested due to his very loving 17 month oldder brother who has the same symptoms. my baby the 3 week old doesnt have a fever but the cough and congestion is just bothering me what can i do for him or should i just take him to the doctors 24 hours before i go to doctors so please respond quickly