Natalia88, I think I am going to go out on a limb here. You display main symptoms as I and I am on the way out from this mess due to my own sleuthing.
I think you may have a trematode infection. Snails generally carry these things, and we know that snails get on everything we eat. Agriculture has a big problem with them.
Anyway, once one of them established, they secrete hormones and other peptides to protect themselves. This causes havoc with the host system "sometimes".
These things also carry parasites, and you will likely have abundant protozoa. ighting this will not always work.
Do you sometimes get a small episode of coughing, then mysteriously goes away?
These things will cause excessive ammonia, and nitrate\nitrite build-up which results in intestinal bacteria to become heavy in gram neg types. This will give you alternate diarrhea with constipation. Oh, the itchy bum is from the high e-coli levels, klebseilla, strep, and of course protozoa, yeast and other fungals.
The fungals, I believe are a result of defensive reactions to changes ecology in lower bowel.
My protocol required prescription medication, but it is new method. I will need to have more conversations with specialist before I can really recommend a protocol,
but I will tell you that the "albendazole" I am taking is doing much of the work.