refuses to chew

My son, almost 14 months old, has been refusing to chew for a few months. Up until 3 months ago, he ate sandwiches and anything you gave him. Now I have to blend his food back into a very fine consistency because if there's a piece that's too big, he starts gagging. It's like he's forgotten how to chew. So he eats his potatoes (very finely blended, no bigger pieces), his fruit puree, and for the rest, he only wants yogurt. Bread, pieces of fruit, anything you need to chew on—he doesn't want to eat anymore. I just show him a sandwich, and he starts crying already. I'm at my wit's end!