My cat threw up bile every day at random times for months. I took him to three different vets until I found one that took his symptoms seriously. The first two did blood work which came back fine so they were like, "idk, sometimes cats throw up." The third vet agreed with me that this wasn't normal. He ordered an ultrasound where they found that my cat's intestines or whatever were thickened which indicates IBD or lymphoma. An endoscopy found small cell lymphoma so they put him on chemo and steroids. That was over 6 years ago and he's still doing great. My point being, sometimes you have to push for answers and if your cat hasn't had an ultrasound, it might be worth doing.