Most of the detox takes place while we are sleeping, your body is asking for time to catch up with the work it has to do. Help it out. Take a nap midday. Exercise - i know this is the last thing you want to do when you feel sleepy, but at least do stretches and try doing so while wearing extra clothing. The exercise will make your metabolism more efficient- the extra clothing will make you sweat and get rid of some extra toxins in your skin.
I feel the same and what I do is I go to the sauna. It helps.