New to this...Question about Vyvanse, Dex | ADHD Information

I am currently on Vyvanse 70 mg w/ 15mg Adderall in afternoon and was
wondering about switching to Dexedrine. I have been having a lot of
problems with stomachaches recently. When I started the medication it
seemed to work--calmed me down a lot. Now that calmness taken a turn
to lethargy I think, I can't get out of bed and I feel completely
unproductive for most of the morning until it wears off which is generally
a long time before I am supposed to take the afternoon dose of adderall.
I thought about asking my Doctor to switch me to Dexedrine since I was
on Adderall XR until it felt like it stopped working (at which point I started
on Vyvanse). Anyway, I would greatly appreciate any insight on these
matters. Thanx.