Hello, Welcome to Health Care Magic. I read carefully your query and I understand your concern. You don’t have to take antibiotics for allergy problem, antibiotics are needed when there is an infection, as you descript here you have an allergy problem from food. For allergy reaction to food you have to take antihistamine drugs that is Benadryl that you mentioned here, saline nasal spray for nasal decongestion, this medication are taken to relive the allergy symptom when they happen (symptomatic therapy), so when you have this symptom you can take this drug, to prevent the allergy symptom happen again you should avoid the cause that you mentioned that is eating a peach, if you didn’t know the cause I recommend you to do the allergy tests. Mucinex is an expectorant, it work thinning the mucus in the lungs making it easy to cough up, it is used for the symptoms of chough and mucus due to cold, flu, normally it was not used to treat cough due to allergy, even it can cause allergy if you are allergic to the ingredient found in the drug e.g. guaifenesin. Hope this answers your question. If you have additional questions or follow up questions then please do not hesitate in writing to us. I will be happy to answer your questions. Kind regard, Dr .Marsida Janko