tom yum soup recipe

1/2 pound shrimp, peeled and deveined 1 cup mushrooms, sliced (button, oyster, or straw mushrooms work well) 2-3 tablespoons fish sauce 2 tablespoons lime juice 1-2 teaspoons sugar 1-2 teaspoons chili paste (optional for extra heat) 1-2 tablespoons chopped fresh cilantro 1-2 tablespoons chopped green onions Cherry tomatoes (optional for garnish)