Blood in stool x2. dad w/ ulcerative colitis, sister w/ crohn's. should i have colonoscopy? if so, can i have while breastfeeding or wait until weans?

Yes: Given your strong family history of ibd, you should definitively have a colonoscopy. Although a majority of the sedatives used during colonoscopy are felt to be safe during nursing, you can "pump and dump" to be on the safe side.

Start with labs: I would start with blood and stools tests that are very good at detecting chronic inflammation. Also they can rule out infection. If your lab work suggests chronic inflammation, i would proceed with a colonoscopy. You may have to "pump and dump" breast milk for a day depending on what drugs they sedate you with--discuss that with the doctor doing the procedure. If labs are normal, perhaps wait.