Hi,
Simvastatin is generally well-tolerated and
side effects are rare. Minor
side effects include constipation, diarrhea, fatigue, gas, heartburn, and headache. Major side effects include abdominal pain or cramps, blurred vision, dizziness, easy bruising or bleeding, itching, muscle pain or cramps, rash, and yellowing of the skin or eyes.
ref:http://www.medicinenet.com/simvastatin/article.htm
This could be an allergic reaction to the drug. It will stop if the drug is withdrawn.