Why does underneath your belly button hurt?

In a normal or healthy woman it shouldn't hurt your vagina when you poke your belly button, not unless you poke it too hard. What you can feel is a discomfort in your stomach that can stretch towards your vagina and it shouldn't be painful; it would feel more weird than painful. But if it is, perhaps you have an infection in your lower abdomen or your vagina that needs to be looked at.