Post ibs after travel in child

My 10 year old became very sick with stomach issues after traveling to Costa Rica. This has been going on since February. He hasn't been able to participate in life since then. We've dropped all activities and barely get school done at home. He taken xifaxan, nortriptyline, ib guard, and now he's on linzess. As his mother it is killing me to see my child suffer all day everyday. I'd like to look into fecal transplant. I'm also wondering if this could be a parasite. We've tested for them but I know they can easily pop false negative on tests. Anyone else give through something similar? Is there a light at the end of this tunnel?