Yes, it sounds like diverticulitis which is controlled fairly easily by diet. However, this is the important bit ...NOT everyone responds well to increased fibre in their diet and you could well be one. I don't - in fact I bloat up with too much fibre and the result is agony!
I am right-sided diverticular, which is unusual - the position your describe is far more typical.
The advice I was given by the hospital to keep this under control is to start with a very bland diet for a few days - a little boiled rice, water and that's about it, then gradually introduce new foods but always kind of bland ones. Then, finally, bring in the big fibres and see what happens. I would suggest your reaction might be similar to mind and I know I cannot eat any apples at all as they are a little bit hard on the digestion. So are cucumber and any raw veg. I love raw veg but have been advised to cut that out completely.
So, porridge, rice and bland soups for a few days to see how it goes.
Get back to me, please!