Just curious- when your baby is sick at what point do you call the pedi?

Elliot's been sick with a cold for the past week and it's pretty minor....only had a fever one day last week, runny nose but the snot is all clear, just a dry cough every once in awhile when he overexerts himself (my little walking obsessed boy won't slow down!), etc. I haven't called the doctor but it just occurred to me this morning...are you supposed to call whenever your baby is sick at all?