Thanks! Hadn't thought of a dermatologist and it might be faster to get into see her than a breast specialist. She can do a biopsy also.
I believe that your best move would be to make an appointment with a Breast specialist or a dermatologist.The symptoms of IBC appear with a swollen breast,redness,itch, warm to the touch, with or without a lump and the skin of the breast becomes like (Peau d'orange) like the skin of an orange.You don't mention if you also have these symptoms.You can certainly ask for a skin biopsy since this problem is not being solved with the antibiotic cream.Since you have a sister that was diagnosed with breast cancer(Good to know that she is a long time survivor! :) )you should pursue this matter until you are fully satisfied with the outcome.Best wishes and good luck.