You can follow a diabetic diet without nuts, seeds, and skins (of fruits and vegetables) which will help you with all your other issues. A diabetic diet is low in fat and helps keep your blood sugars down, The avoidance of nuts, seeds, and skins will help control your diverticulitis. Suggest going to the American Dietetic Association website, www.eatright.org to find a Registered Dietitian (RD) in your area that will help you with a diabetic diet meal plan or contact a Diabetic Center where you live for help. Thank you for your question.
A partial answer, since I don't know all of what you have to avoid, would be that a diet based on the whole foods concept should help some. The whole foods concept is based on the idea of eating foods as close to how you get them from nature as possible without processing them. Going gluten free has helped several of my conditions, including pre-diabetes. I went gluten free for other health reasons and had many benefits. I would have worse female problems than I do if I hadn't gone gluten free. If it's not endo, there is still something going on down there. However, it's far less severe of symptoms after going gluten free. Going gluten free for me has been in addition to the whole foods concept. I'm not sure if you can eat quinoa with diverticulitis, but it is helpful for diabetics in that it does actually have more useable protein than wheat does. The doctor or nutritionist might know if quinoa would be alright for someone with diverticulitis. It is good for diabetics, though, since it does help to stabilize blood sugar levels.