Its not uncommon. Many times caused by drinking coffee or soda ( 'Many adults with ADD/ADHD have lifelong love affairs with coffee or caffeinated sodas. Yet caffeine may exacerbate the effect of stimulant medications, creating anxiety and heart palpitations. You can’t determine what’s causing these side effects -- the stimulant or the caffeine -- unless you gradually wean yourself off caffeine before starting stimulants. (Try to do it a few days in advance, though, so that you don’t mistake a headache due to caffeine deprivation for a medication side effect.)
“Some people can tolerate stimulants and still have some caffeine,” Weiss says. “For others, caffeine interferes by creating or exacerbating side effects, making it impossible to increase the stimulant to therapeutic doses.") from http://www.additudemag.com/adhd/article/8942-2.html
If this is a recent change, I would think that you also have changed something else recently like the dosage? or diet? The other question is when does it happen? And how often during the day. IR's release at different times. The highest dose of meds is always released at the start of the medication - in the first 30 to 45 min. If your problem is happening later in the day, then something else is probably also a factor.
Here is a link to a pretty good site on side effects. You might find more info there. And perhaps with more info, I can give you more ideas. Hope this has helped.