Tami-
We just went through the very same thing with our 2.5 y/o this early August. She is prone to horrible sinus infections/ear infections so we were going to fore-go the flight all together if we couldn't see improvement. But Children's Benedryl is a miracle drug. We get her the chewables and crush it and mix it with chocolate pudding. She never knows it's in there. Often we only give her 1/2 to 3/4 of a 5mg tablet and it does the trick. It dry's her up and she rests much better. We have been able to elude the dreaded sinus infection/ear infection since we have been doing it. I would never condon giving this drug without cause but since our pedi. gave us the go ahead we have been comfortable with using it.
She had no ill effects on the flight and never complained once when we took off or landed. I braced myself for the worst and nothing happened. I also gave her Tylenol before the flight per doctors recommendation.
Good luck and hope all goes well.
Sincerely
J.