I'm stopping Elavil and am EXTREMELY fatigued, any suggestions to counteract this symptom?

I have been taking Elavil for quite some time to help with the depression and anxiety that comes with Fibromyalgia. I was recently prescribed a 12 mcg fentanyl patch, and am doing rather well with the pain aspect. I am weinig myself off of Elavil. I was taking it to help with coping with the pain. Now that the pain is under control, I feel like I no longer need it. I've actually been doing rather well, and am down from 50mgs to 12.5mgs. BUT, the fatigue is horrible! I have a 5 year old who is in school all day, but I also have a 3 year old that demands lots of attention. Why does this last little bit seem to be affecting me so much? I have no other withdrawal symptoms.