How should I follow up a job offer?

It's been two and a half weeks already since I signed papers for the company. They told me that my starting date would be on the 22nd of this month and they'll contact me soon (without any specific date). A friend of mine who works in the same company told me that I'll be needing to take a medical examination before actually starting. I haven't got a word about it from the HR though. The question is, how should I ask for an update about my application/hiring status? Is it normal that they still haven't called me? I'm getting kinda anxious already and idk what to do.

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