Could walking in cold air cause an ear infection? I have pain in the r ear & going into neck. Last dr visit she said I had fluid in r ear a week ago.

No. Middle ear infections are caused by germs that enter through the drainage tube connecting that space to the throat. Not cold air. If there is already some fluid, it could become infected in a few hours or never.
Cold air. Not usually. Ear infectionudually result from backing up of mucus from the nose.