yello water drain suddenly with vary bad small on left nose at time 3 to 4 drop

Since 4 days I have cold… but now since 2 days yello water drain from my left nose
Which has vary bad breadh. Full day that bad bradh smell remain. The drop comes out when I
Band or my forhead on down ward…ie. to tie shoe lace or pick glass of water from ground on standing position. Pl advice…