My son is 20 months old, he has a dry cough, runny nose and he sounds like he has a cold when he talks. No fever and it doesn t seem to be bothering him when he is playing, I was wondering if I could give him childrens Benadryl, I am thinking he might just have allergies but im not sure. It says on the box to ask a doctor if younger than 2 years. He weighs 34 pounds maybe a little more.