A couple of years ago I had chest infections, cough, general washed out feeling for months off and on. Since then I have done my best to keep fit with gym and swimming plus lots of walking in the fresh air. I haven't really been ill since (though that's no help to you at the moment I'm afraid).
However I have also noticed that since I have had to take a daily antibiotic for frontal fibrosing alopoecia this also corresponds with my illness free period. It hasn't stopped the hair loss at all but a few signs of impending cold or a sore throat have all been nipped in the bud. I know doctors seem to infer that antibiotics do not help colds but I am wondering.
Hope you soon recover and meanwhile the usual advice, lots of fluids, rest, warmth, maybe honey and lemon (or something stronger!)