Jenn, usually a breast lump that grows noticeably larger, quickly, is more likely to be an infection. However, with the itching, and nipple retraction, and the quick growth, AND the lack of effect from the first antibiotic - yes, I'd suggest you get a second opinion. Waiting 3 weeks for more screening, when the situaiton seems to be evolving so quickly, isn't a good option.

If at all possible, see if you can schedule an appointment with a breast specialist; they're often found at cancer centers. Even better would be an appointment with a breast specialist at a Comprehensive Cancer Center, a hospital designated by the government as being top-quality. This would be your best bet for getting this issue diagnosed and treated successfully, and quickly. Good luck - PJH