Did you continue to nurse or pump and dump during the time you were taken the medication? Did LO start to not nurse well?

I was just prescribed this for a breast infection (mastitis) by my OB/GYN and was encouraged to continue to breast feed, however dynapen is a class B drug, which does pass into the breast milk. It's in the penicillin family and I'm not sure if I want DS to nurse while I'm taking it. I took 3 pills so far and DS seem to not be nursing well (which could be from the clogged duct) and he is a total bear! Fussy, not sleeping, etc. I gave him a bottle of frozen milk and he ate much better... Maybe I shouldn't even take the medication? I feel much better today, less flu-like, but my breast is still sore.