My cat vomits after eating or drinking. Sometimes he repeats vomiting once it starts. He doesn't particularly look like he's lacking energy - he's been vomiting pretty often ever since we adopted him at a year old. He's infected with FeLV, but we haven't seen any abnormalities after 8 years of treatment. He hasn't been losing weight either. I am concerned about the vomiting but our vet tells me there aren't any noticeable issues. I take him to the vet every 4 weeks for interferon treatment.