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How do you know if you have fluid in your knees? - physical fluid dynamics by tritton

I went to the doctor for pain and thought it was mentioned in the knees fluid, but never. She even said she was, she prescribed physical therapy only. I thought that since he is the doctor knows what he's doing, but you know, a friend who works at the clinic, said that if I believe that the document is not a good idea that you should get a second opinion elsewhere, because they are wont to make mistakes. Now I do not know what to do. It feels wrong to go against doctors orders. I therapy, 11, should wait to see what was said by the therapist?
Thank you for your opinion!