What are FODMAPs? Can it cause abdominal cramping, itching, nausea, loss of weight?

Possibly. FODMAP is an acronym for"Fermentable, Oligo-, Di-, Mono-saccharides And Polyols." These carbohydrates are commonly found in the modern western diet. These are short chain carbohydrates (oligosaccharides), disaccharides, monosaccharides and related alcohols that are poorly absorbed in the small intestine, which are associated with irritable bowel syndrome, and functional leaky gut syndrome.
Light My Fire. FODMAPs are certain food elements that are poorly absorbed in the small intestine.So they stay in the intestine and are chewed-up by the bacteria in there which produces a lot of gas(it's called fermentation).This is complicated and you need to do more research(try Wikipedia to start) Check out foods to avoid. Meanwhile if you get gas, don't play with matches!