Ive had about 5 episodes of diverticulitis since may....keeps returning monthly. does surgery mean a colostomy bag is necessary?

Probably not : It's likely that you won't need a colostomy. It depends, however, on which parts of your colon are involved. Usually the disease is most significant in the sigmoid colon. It can usually be removed and a new connection (primary anastomosis) created without the need for a colostomy. I'd suggest you see a surgeon, go over your imaging, and discuss the options.