What you have described is a symptom of caffeine withdrawal. Caffeine withdrawal can present as headache, tiredness and fatigue; mood changes including depression and irritability, difficulty concentrating, and flu-like symptoms, which consist of nausea, vomiting and muscle aches. These symptoms can occur alone or in combination and can last for several days if the person does not have additional caffeine whether it is in the form of tea or coffee or any other source of caffeine. My suggestion is to decrease the strength of the tea you drink. For instance, if you make tea in a tea pot with 2 spoons of tea, use one and 3/4 spoons, wait 1-2 weeks and then decrease the amount of tea again and so on. You may find that you may have periods of irritability and some of the symptoms described above as you decrease the amount of caffeine. As your body adjusts to the lower amounts of caffeine these symptoms will slowly go away.