Any old probiotic wont have the same effect as S. Boullardi. It doesnt just crowd out the bad guys, it eats them. And has a healing effect on the intestine wall AND raises sIgA. Look up sIgA and its importance. You’ve been sick for so long it has to be very low which is part of the problem. Getting sIgA up is one of the tricks to getting over bowel disorders.
Your gastro sounds useless. You dont need a integrative gastro, just a GOOD integrative doctor. Someone that understands the whole body, treats it holistically, and knows all the good tests and treatments available that allopaths are told are no good by the industry that brought them up.
Any doctor that is going to actually help you uses that test already. In fact, that would be a good question to ask to filter out the docs you dont wanna see.