Dull hair usually means product build up. Do you clarify your hair? Try using a warm water/baking soda mixture and it helps to get rid of product build-up and it makes my hair sheeny.

Also are you doing regular deep conditioning treatments? I am not sure where you live, but if it's cold and you where you hair out a lot, you should be doing deep conditioning treatments at least twice a month if not every week. Adding a little oil (such as grapeseed oil) and/or honey to the deep conditioner and provide a good treatment for your hair.