Ear infections are not always easy for a parent to diagnose, because the symptoms can be vague and mimic those of a regular cold or flu. In fact, ear infections often start as a cold with a cough and a runny nose. A cold virus causes the entrance to the eustachian tubes to swell so that it's easier for fluid to get trapped and infected. The next thing you know, your baby has a fever and is becoming more irritable. He may also pull on his ears and seem crankier when lying down, because this position causes the fluid to push on the eardrum, resulting in more discomfort.
The only way to be sure that your child has an ear infection is to visit your pediatrician. Take a baby younger than age 2 to the doctor if a cold and apparent discomfort don't go away in two or three days, or if a fever doesn't go away in one or two days. (If your infant is less than 4 months old, notify your doctor of any fever immediately.) When your physician peeks in your child's ear to check for signs of an infection, she's looking at the eardrum to see if it is red, thick, or bulging.