i breastfed my son while flaring for several months. i got really skinny and he got nice and plump and healthy. and once i was diagnosed and on some meds, i did gain some weight back.
but there are no ill effects for nursing baby while you are flaring, as long as you are staying healthy enough to care for him (obviously).
try this link to find out about specific drugs and safety with nursing.
your GI is the expert on your gut, not lactation. the book 226 mentioned is a great resource, as is la leche league (you can find them online and they also have a toll free 24 hour number now as well).
your OB and pediatrician will also have some drug/lactation info and it's good to get more than one opinion. in my case, my OB and pediatrician actually talked to each other at one point to discuss the meds.
are you still on pred? how bad is your flare right now?
29, happily married, stay at home mom to 2 year old son. due to have baby #2 9/17/08
UC (probably pancolitis, but no c-scope yet), diagnosed June 2006, started having major symptoms sometime in January 2006, about 3 months after childbirth. 2nd flare (minor) may 2007 after taking caprylic acid for 2 weeks.
-Prednisone 8/28/06-2/28/07. and again may '07, 8 week course.
-Prayer! asacol, probio, ground psyllium husk, prenatal, folic acid, cal-mag
may you live all the days of your life.