Request Dr’s note to leave on maternity??

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Hey ladies I’m a FTM I’m 33 weeks pregnant and my HR suggests for me to ask my DR to take me out of work already... I have been having really bad back pain and swelling I sit on my but 8 hrs a day and it’s exhausting... next week I have an apt with my dr and how can I ask her to take me out of work and start my disability and also how does disability work?? 😩 I’m so confused pls help