Hi,
You have done such a good job with your little one - it is a heartbreaking position to be in. But, overall, your baby needs you to be as healthy as you can be. so, if the decision is that you must stop breastfeeding, then I hope you know what a wonderful job you have done.
However, I would suggest that ASAP you ring Rodney Whyte, head Pharmacist at the Monash Medical Centre Drug information Centre on (03) 9594 2361. It is my understanding that you could recieve cortisone/steroid therapy whilst continuing to breastfeed.
If you need any help, feel free to send me a private message