Try the shield for a feed or two and see if it helps. Don't use it on the good side, and just use it until the crack heals up.
If the crack takes a long time to heal that may be an indication that you need more than the antiobiotic (perhaps a different antibiotic, perhaps an anti-fungal cream of some sort), so if in a few days there is no improvement then go back to the doctor.
Another option is to express from the sore side and then bottle feed - but that brings another set of issues with learning to express effectively and with bub learning to switch between boob and bottle.

Australian Breastfeeding Association - Breast and Nipple Care