I Have An Older, 14 Yrs., West Highland Terrier. When

I have an older, 14 yrs., West Highland Terrier. When he eats, sometimes he pants, make a groaning sound on the exhale. He will, occasionally, throw up, making an horrifically loud sound. I changed his food from lamb and rice, to a Science Diet - good for the kidneys, brand about two to three weeks ago. But, his symptoms started before that. Any ideas?