Dextroamphetamine making me sleepy

My Dr just started me on 5mg Dextroamphetamine IR. (Generic Zenzedi/Dexedrine) I'm on day 3. And it's making me tiiiiired! Like I could nap all day on this med lol. Anyone else experience this when you first started taking it? Did you find that you needed a dosage change or just time to get used to the med?

I was taking Vyvanse but my new insurance doesn't cover it so we're exploring other options.