I just need to know if a low does antidepressant with Vyvanse (lisdexamfetamine) helps to not get the depression when you go off the Vyvanse (lisdexamfetamine) for weekends?

Off-label. This would be an off-label use of an antidepressant. Psychiatrists sometimes do use medications in off-label ways, depending on circumstances. Still, antidepressants used only on weekends would not likely help much, since they usually require consistent dosing for 4-6 weeks to show effect.