How do i know if im having a diverticulitis flare up or ibs? i've been diagnosed with both. i have nausea, bloating, bloody stools, lightheadedness?

Abd pain: Should see your doctor as distinguishing one from the other is difficult without an examination.

May be neither: How were you diagnosed with either. Even though you are young I assume you had a colonoscopy to rule out colitis and a CT scan to confirm diagnosis of diverticulitis which is uncommon in 30's. I say this because bloody stools are not usually seen with either of these.