What can I do if a walk-in clinic doctor clearly misdiagnosed my illness?

I went in to my local walk in clinic with all signs of head cold/ sinus infection. My head was hurting, I had a stuffy nose, and phlegm. He did a test and he said it was the flu. If I had the flu or Covid I would be bed ridden for days. My body isn’t good with illnesses because of my medical issues.
I tested at home multiple times and it came back negative multiple times. I went back to clinic to show them and the doctor said that they were bad tests. The girl at the front desk that was sleeping said she seen the test too.

What can I do if a walk-in clinic doctor clearly misdiagnosed my illness?
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