Why am i afraid to eat food?

I am more than a picky eater. There are very few foods that i eat. I am 14 years old and i weigh 98 pounds which i think is very underweight. I only eat foods like Tacos, Burgers, Pizzas, Steaks, only things that i know through experience taste good. Whenever i see something that looks different, anything from salad to stew, i turn it away because my immediate response is that it tastes bad, without actually tasting it. I am also restricted to my house because i cant go over to my friends house because i don't know if i will like what they are eating. My mom always asks me " what do you think will happen if you eat something different, are you going to die?" I always say now but its more complicated than that. Its also embarrising when we have company and relatives over for dinner and they ask where i am, and i am in my room because i am afraid to eat whats for dinner because it is different. I am starting to be concerned about my health and i practically cry whenever I eat something like McDonalds. What should i do?