'Pica mucho', something is giving you a rash and you must scratch yourself

I agree with Kylecito but in some latinamerican countries it refers to a person or a thing that is very annoying to us. Bye.

Like Kylecito's answer, "It's really itchy" means just "pica mucho", " es muy picante", more related to skin than meals (chile, spicy foods, etc.) Like Teresa said, it also means something you feel very uncomfortable with, like bugs, clothes, annoying people, etc.