Can you get a flare up of ulcerative colitis?

Absolutely. Flares of ulcerative colitis(uc) are quite common and can be brought on by other illness (cold, flu, etc), medications (ibuprofen, aspirin, alleve, etc), missing doses of your uc meds and sometimes for no apparent reason.
Yes. Ulcerative colitis is an inflammatory bowel disease in which your immune system cannot control inflammation. There are meds that help keep the inflammation under control but flare up can occur. It may be possible that current meds may need to be adjusted. Be sure to see you doctor about flare ups because ulcerated colitis can continue to spread throughout the colon.
Yes. Both uc and crohn's are characterized by periods of active disease and remission.