In addition to ed's comments essential tremor (cause unknown) is the most common type of tremor. In general, tremors occur when there is a problem with the nerves supplying certain muscles. However, everyone has some essential tremor but the movements are usually so small that they can't be seen.
Hypoglycemia - usually episodes of tremor with hypoglycemic attacks. Hypoglycemia, which is caused by low blood sugar, and symptoms of hypoglycemia may include anxiety, sweating, tremor, palpitations, nausea...
You should contact your doctor to rule out any serious condition such as liver, kidney disease. Take care and thanks for your question.
The first thing which strikes me is your Lipitor regime. I assume you are taking 20mg in the morning and 20mg in the evening? This is really pointless. Lipitor is well known to work while you are sleeping, because the Liver makes most cholesterol at this time. Other statin brands can be taken at any time, probably because they sit in the blood for longer or something, but Lipitor strictly instruct you to take in the evening.
There are many reasons for trembling/shakes, perhaps your Dr should start with a blood test to look at your electrolyte levels. These are metals which you consume in food and assist the nervous system in conductivity. A lack can cause shakes and make you feel somewhat lethargic. I used to take a tonic years ago, I think it was metatone tonic which was a syrup containing all kinds of metals. It was like a magic medicine, really boosting you. Not sure if anything like that is still available.