I will start with the theory of what is wrong with us.All of what I say is from respected medical authorities and I implore you to read read read!All of it is online and accessible.I have spent countless hours reading and have become convinced that we are suffering from a form of dysbiosis.
Our microbiota(microbial community of bacteria,virus',and other unknown organisms) in our gastro intestinal tract has been severely damaged by over use of antibiotics,antivirals,other strong meds,poor dietary variety and a predisposition to be sensitive internally to chemicals.
The reason why we can not get better is that,the proportions of good and bad bacteria are completely off,and some critical species are most likely extinct or at levels that are too low to do their task.We also have the possibility of being poisoned by toxins excreted by some.
One example of:Why do we all seem to have different yet similar symptoms?Because the microbiota is completely different between one person and the next.Even identical twins have hugely different communities in their gut.It is almost as different as DNA.
With all the differences in diet,medicines,DNA, age,....But,they control your immune system and they have been descimated by modern medicine and poor diet variety.I will continue to write part 2:the treatment!