I agree with others : you MUST consult your GP and have all the tests required. However there are no tests for IBS, other problems have to be eliminated, and when there is nothing else left to blame, they decide it is IBS.
In my case (over 30 years ago) nothing the GP prescribed was any help, in fact on one occasion the GP said he could provide a cork, which was not exactly helpful or re-assuring. Keeping a diary of what you eat is the important thing, not going by what causes IBS in other people - everyone is an individual with individual intolerances. In my case : lactose, fruit skins (tomatoes, cherries, peaches, grapes etc), most breakfast cereals. All the things I really enjoy. If I ate any of these things I would get the most embarrassing diarrhoea and pain.
I eventually discovered Lepicol - look up their website. I can now eat many of the things that disagreed with me as long as I am careful and don't over-indulge. Lepicol is harmless and works for people who are constipated and those who are "wet and windy". I do not own shares in the company, and know no-one who works there, I am simply very grateful that there is a product which transformed my life and made it "normal" again.