Bummer, Crankin! I would be just as frustrated as you since we eat very similarly, from the sounds of it. And doubly frustrated to think that you may have had this for decades and never been diagnosed.
One of my besties growing up had diverticulitis and had to be on a SUPER low fiber diet. Back then, that was how they treated it. Forever. So perhaps it's for the best you weren't diagnosed back in the diverticulitis dark ages! I am out of touch with her now but remember reading somewhere that doctors had totally changed their tune and now recommend a high-fiber diet. I can see where they might recommend low fiber for a flare-up, though, just to let the intestines rest. Just like when our dog has GI problems! 
Hope you're feeling much better soon.
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow