Flatulence is often due to changes in your diet as you have mentioned. Beans, onions and other spicy food are very often the main causes. I would recommend that you avoid colon cleanse as you do not want to disturb the 'friendly bacteria'. In terms of medication then peppermint oil capsules or charcoal tablets can be helpful and I would also recommend that you have peppermint tea after meals.
You should avoid carbonated water or soda. And the other thing is to ensure that you minimize swallowing air with loose dentures by getting a dental review (if you wear dentures).