Hi LMR, have you been diagnosed only with ADD? Do you have a secondary diagnosis as well?

Assuming you have a therapist who has diagnosed you, I think you should tell him/her about this lack of focus, especially if it might be a side effect of the Zoloft. The therapist might want to modify your medication(s) based on what you have shared here. I encourage you to share this with your doctor. I hope you can get some relief.