At last week's 6 month appointment I mentioned it to the doctor.
Did you know that coughing can be a sign of food allergy in a baby? Neither did I!
After a bit of experimentation we realized he was likely reacting to apples. We removed apples from the rotation and the cough has gone away.
So now we wait a month and try apples again. If Nicholas still has a reaction we try again after he is a year old.
By the way, I have also never heard of anyone being allergic to apples!