Doctor won’t increase my dose 40mg LisDex

So I’ve been on 30mg of Vyvanse for 4 months and when I told the doc it wasn’t lasting as long as I need it to, she said that I’m reacting to the “second salt” in the Vyvanse; wdym second salt??? There’s only dex to my understanding. On that note, she only increased but said I can’t increase for the rest of the year. This made me upset because 40mg barely works for me. I have to take 60mg to really feel my brain work with me. It makes me upset. What do i do?