Hello, I've Been Having Strange Things With My Body Over

Hello, I've been having strange things with my body over the last few years but it's gotten worse throughout last year to this year. every now and then I get horrible cramps it feels like gas building up more in my chest area though. Along with that I get weird digestion problems and constipation occurs. A lot of times when im in public places I start feeling nauseous and all of these symptoms start to occur all at once, the gas building up in my chest/stomach, I feel like im about to vomit and then I start salivating a lot but I never end up vomiting.