Poor sleep on Dexamphetamine

Hi All, I was diagnosed with ADHD 3 months ago and have been on Dexamphetamine since then. I’ve found that 10mg per dose works well for me. Each dose only lasts 4 hours so my doctor has put my daily dose as 10mg 3x a day. However if I take my second dose later than 12pm I have a really hard time sleeping (which means I can’t take my third dose either without poor sleep). I have no issues getting to sleep but will wake up in the middle of the night with my thoughts racing and take several hours to get back to sleep. My doctor prescribed me 4mg of melatonin per night which I’ve been taking for 2 months but it hasn’t helped. I’ve read that it’s useful for helping to induce sleep but not stay asleep. I was wondering if anyone had any advice or experience with this? Or what other peoples experience with sleeping has been like on different medications? I was hoping to get put on vyvanse but I’m worried the problems will be the same or worse as it’s long acting. Thanks!