Hey Annabelle, welcome...I wanted to comment on the parasite issue. Generally speaking, acute parasitic infections are characterized by symptoms such as high fever, profuse, watery diarrhea (up to 20-30 times per day), vomiting, rapid weight loss, etc.
There is one, though, called Giardia lamblia; it's an especially common parasite (even found in the U.S. on a regular basis) and can cause bloating, gas, and foul-smelling loose stools...so that'd definitely be worth checking out. It's highly treatable with anti-parasitic/bacterial drugs like Flagyl and Ciprofloxacin.
I lived in Africa and had a chronic parasitic infection for years where I had diarrhea 20-30x/day, intermittent fevers, weight loss, etc. and it was miserable...I was initially diagnosed with Giardia and amoebic dysentery, and who knows what else was in there! I was treated with Flagyl and Cipro so many times I've lost count, but I'm finally better.
Sounds like you've had gut issues for a while; it'd definitely be worth getting a colonoscopy and giving three stool samples to your local microbiology lab for their perusal!
My IBS-C symptoms started about 5 months after emergency surgery to remove gall bladder. Gastroenterologist says no connection, but I still believe that was the trigger.