My poo has been yellow for a week, what could it be?

Not concerning.: Stool color can vary because of a lot of factors, most notably diet. It is generally not a concern unless the store is bloody or solid black in color, due to bleeding, or rarely very pale due to gallbladder problems. If it persists to be a change in your usual color despite eating your normal diet, you might mention it to your family doctor. Otherwise, it will likely return to normal. Good luck.