My teeth are gettig yellowish, why?

I don't drink Coffee or alcohol, and I don't smoke, so I really don't know why my teeth suddenly began to change color. I did change my toothbrush from the normal ones to the ones that have like those hard thing in the sides that are suppose to clean among the teeth better, and I had been using the arm and hammer toothbrush but now I am using crest (which I thought was better) and useing mouth wash. I tought all this was going to improbe my teeth but ever since I made the changes they have gone yellowish. Why did it happen?What do I do now?