Good question for a pharmacist. Could be situational; could be a lag in effectiveness, and probably a few other things.
Pharmacist may tell you to keep taking it a while longer, or may tell you to call doctor immediately.
Switched from Adderall IR 60mg daily to 60mg of Vyvanse daily. Worked for a few days but now I have brain fog, depression, lethargy, no motivation, no social ability, and feel dull. Good appetite, hydration, no alcohol. Dose too low?
Mood swings (depression) is a common side effect of Vyvanse. As others suggested, this is something you should discuss with your doctor. I'd also suggest alternative remedies since they don't cause many side effects and may provide satisfactory results (depends).
Take a look at some of the herbal brain enhancers at MHRC and talk with your doctor about using such herbs as a complementary or alternative treatment. Although they don't always work, they are worth trying before more advanced drugs are used.