What you describe sounds like it could be diverticulitis which is what diverticulosis can progress to; however, only a CT scan would provide definitive proof if the condition had actually progressed to diverticulitis (not that I am recommending the radiation, mind you). Though there usually is no substitute for a professional diagnosis, I have often thought that the diagnosis of "diverticulosis/diverticulitis" sometimes is one that doctors use instead of saying "I can't figure out what you have for sure".
The same symptoms you describe could also indicate inflammatory bowel disease or stomach ulcers, and thus you might try some natural remedies for those to see if they could help. If you have diverticulosis which has not progressed to diverticulitis then the healing and colon wall strenghtening provided by some of the remedies (such as colloidal silver and vitamin C could help you remedy your condition.
See:
http://www.tbyil.com/IBD_Natural_Options.htm
http://www.tbyil.com/Ulcers.htm
Beetroot juice is good for keeping the colon cleansed.
Also, when you have an onset of pain drinking a glass of water may alleviate or eliminate the pain within half an hour or less.
I hope this helps.