This is Dr. David
blood testing can check if your kidneys are functioning properly. and if you have normal BUN and creatinine levels.
abnormal thyroid hormone levels can cause dry skin and bouts of itching skin on your body.
you should ask your doctor to check your thyroid hormone levels.
metformin can often cause itchy skin as well.
you should get your liver enzymes checked regularly if you are on simvastatin.
let me know if you have other questions.