What causes leg’s uncontrollable shaking? HELP Please?

My dad is 50 years old, he started having subtle leg pain around his thigh, few years already,

he didn’t pay attention in the beginning as it was not a sharp pain and didn’t disturb him much,

a couple years ago he had a bit swelling and he used to feel a bit pain when sitting down or sleeping.

He went to doctor but doctor couldn’t find anything wrong.

About 7 months ago, he started leg shaking and now it got worse, his leg shakes uncontrollably when he’s resting.

Anyone has an idea what it is and how to cure it? He goes to doctor tomorrow but I don’t have a trust in these doctors, it could have been avoided if only that doctor paid it more attention and gave a correct diagnosis.
What causes leg’s uncontrollable shaking? HELP Please?
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