Does Taking Amitriptyline Cause Difficulty In Concentrating And Mood Swings?

My 9 year old daughter was recently prescribed Amitriptyline for headaches/possible migraines. She started the medication approximately 3 weeks ago, 1-2 pills at bedtime. This week her teachers have commented that she seems to have trouble concentrating. I have noticed she seems "moody" and more easily upset. I was wondering if this might be a side effect of the medication?