Talk to your doctor, but the simple answer is to take more. Vyvanse has a half life of about 12 hours, so if you take it in the morning then by evening the medicine is starting to heavily breakdown. It’s pretty common for people to take more at lunchtime to get them through the evening for that reason.
If you’ve ever looked into email protocols you’d find it’s a nightmare of cludged together solutions piled on-top of each other over decades. It simply isn’t designed for instant messaging.
Here’s a great talk that goes into a bunch of issues with email in general.