Fatigue or Depression?

Fatigue is a sign of depression. Depression is a symptom of MS. Fatigue is a symptom of MS. Soooooo, how do I know if I'm tired because of my MS or because of depression? I suffer from both at various times and to various degrees, but are they related? Is it a cause and effect? I decided it doesn't matter. I will keep taking the antidepressants and keep treating fatigue the best I can, no matter why I'm tired. I drink energy tea, I take naps in the afternoon, and if it that doesn't help enough by late afternoon, I eat peanut butter or a granola bar or other such energy enhancing foods. Of course, none of this can help if I'm too tired to get up in the first place, which is often the main problem. But most days I can drag myself out of bed and get going pretty well to make it through the day. On days when I can't, I call in tired...I mean sick. But that is a topic for another day.