Firstly most people think they are allergic to a specific drug but in reality they are not .
A diagnosis of Drug allergy needs formal testing in which small amount of the drug is injected into the skin over the forearm and we wait till any reaction develop to the drug like:
Hypotension (sudden fall in BP)
Tachycardia (fast heart beat )
Shortness of breath
Rashes all over the body .
Next Steps
if you are truly tested as penicillin allergic then the answer to your question is erythromycin you can use it as an alternative to agumentin.
Health Tips
please use antibiotic only after being prescribed by a doctor as they have side effects .and unessary use causes antibiotic resistance which simply put if the same drug need to be used for you in the future for some other infection probably erythromycin wont work for you . You have to go for higher antibiotics