What would cause formula to shoot out of my 3 week old daughters nose while feeding? What should we do?

Eating too much, and spitting up, if they cough, if they sneeze, can all cause food to come out of the nose. The nasal passage and throat are all connected, so this is just what happens in babies. While perhaps not common it is very possible.

If it keeps happening, I would take the child back into the doctor