is this Vyvanse side effect or flu?? | ADHD Information

just wondering if anyone has had experience with side effects of Vyvance.  My 5 yearold son started on Nov 1 with 20mg/day.  For the first couple days he had a little nausea and dry mouth but both seemed to go away after a few days.  We saw a small improvement in his behavior and impulsivity but were advised by psycologist to try 30mg.  I gave him 30mg yesterday morning and by 4pm he was vomiting every 20 min for hours.  I gave him a little gravol and he slept for 2 hours and woke to vomit every hour till 3 am.  He woke at 7am feeling fine, lots of enery and ready for breakfast (so he said, although he didnt actually eat).  I game him another 30mg about 8am and now by 1pm he has a stomach ache and is vomiting again.  The stomach flu has gone thru our neighbourhood a few times in the last couple weeks and our family never caught it.....I am having trouble deciding if its a bad reaction to the meds or has he caught the stomach flu??????