Sudden changing of such drugs can lead to side effects. First of all you need to describe your symptoms and illness only then we can answer whether you need atomoxetine. If you have adhd it could work however in case of any other disorder i would suggest you consult a psychiatrist.
Next Steps
Dont change such category of drugs on your will. Consult a psychiatrist. To improve focus there are other techniques as well like writing things down, remembering things in sets, chunking, etc.