Doctors trump labels. Each and every single time.
(labels used to read 6mo and under consult your doctor, and guess what? 1mo were given the go ahead and given correct dose)
That's what doctors are for. He can't prescribe it, as it's not an Rx med. Instead he tells you to buy it and what the dose/rate is. If it WAS an Rx med, he'd just prescribe you a bottle of it.
DO know that in every other 1st world country Benedryl (and pseudoephedrine, and tylenol, and ibuprofen) are still sold in 'infant drops' with the correct dosing per weight (not age, never go by age) on the back. Your ped may have goofed and just forgotten the correct dose per weight isn't on the back of infant drps any more. (pulling infant drops off the shelves in this country is still pretty NEW... they've been safely used for decades, it's only the past couple of years they've been pulled. And they weren't pulled FEDERALLY, it was a voluntary recall, following some studies done after pseudoephidrine was put 'behind the counter'. A MINORITY of parents were doing 1 of 2 things:
1) Not reading the active ingredient list and "double dosing" (as in giving tylenol cold, AND tylenol... or 2 cold meds with identical ingredient lists)
2) Kept giving the same med over and over or in higher doses because it 'wasn't working' (because there is no decongestant on the shelves anymore. The "PE" meds changed to an antihistamine which does NOT work at clearing congestion from infections, just allergies. Because it didn't work the MINORITY of parents just gave more and more).
NEVER EVER EVER EVER take "our" or ANYONE ELSE'S dosing recommendations unless they are a doctor or pharmacist or consulting nurse! If both your doctor and pharmacist happen to be closed, call the 24/7 nurse advice line and say your doctor said to give you 22lb infant benedryl but you don't know the correct dose. They will look it up for you.