Bring a medium pot of water to a rolling boil; add the raw shrimp and cook until pink and opaque, about 2–4 minutes, then drain and set aside.
Meanwhile, make the cheese sauce: in a medium saucepan over low–medium heat, combine the Monterey Jack, cheddar, and cream cheese, stirring until melted and smooth.
Stir in the 1/4 cup milk a little at a time to thin the sauce to your desired consistency, then keep warm over very low heat, stirring occasionally.
Preheat the oven to 350°F (175°C). Spread the tortilla chips on an oven-safe plate or baking sheet and heat in the oven 5–7 minutes to crisp.
While the chips heat, make the pico: combine the diced tomatoes, finely chopped red onion, minced jalapeno, and chopped cilantro in a bowl; stir to combine.
Assemble the nachos: spoon the cheese sauce evenly over the warm chips, top with the cooked shrimp, then spoon the pico de gallo over the shrimp.
Garnish with sour cream and sliced fresh jalapeno before serving.
