Why would they prescribe me this!?

I called my OB today because I have a bladder infection from the catheter used during the c-section. I informed them that I was feeding my son breastmilk. My doctor called two prescriptions in. One to relieve the burning associated with the infection and an antibiotic.

I took my first dose, pumped some milk, and then read the papers that came with the medicine....It states DO NOT breastfeed children under 1 month old while taking this medicine. The other medicine it says that no studies have been done on breastmilk.

I just don't understand why he would prescribe me that medicine, knowing I was feeding my son breastmilk.

I've taken some antibiotics that stated not to take while pregnant. It's a benefit outweighs the risk type thing.