Suggest Medication For Erythema,swelling And Mild Tenderness At The Site Of Injection

I had a SQ pneumovax injection yesterday and developed swelling, erythema, mild tenderness and warmth around the injection site. Saw the PA in the employee health clinic at work and was put on Zithromax. prednisone and Zantac. I took two Zithromax today and am to take one daily for four more days. It has spread some and covers an area approximately 4"X3" on my LUE. No fever, not particularly painful. One surgeon who saw it thought it was an allergic reaction rather than cellulitis but there is no itching. I am somewhat concerned by it's progression towards my elbow. How soon should I expect to see regression of the erythema? Thanks.