Been on Dexamphetamine (ADHD) 5 months, no dose changes but suddenly showing signs I'm on a too high dose?

Been taking 2x 5mg Dexamphetamine tablets for 5 months now, been to the doctors a few times since being on them and had surgery and my blood pressure and heart rate were fine then all of a sudden starting from around 2 weeks ago I started getting hand tremors, cold fingers, sweaty palms, shivers down my back and sometimes light-headed... haven't touched the dose at all... doctor thinks it's possibly the Dexamphetamine OR a heart problem (whch is being looked into) is it very likely my body has suddenly decided that I'm on a too high dose of Dexamphetamine?