Baby cough

Bakit po kaya ang baby ko hindi nawawala ang ubo almost 1month na nkaka 4 na check up n kami we've tried giving her ambroxol presc. By pedia then nung nagka plema sya is klariththromycin nging ok naman after 3 days nawala then bumalik ulit... i don't know what to do.. pina xray n nmin sya.normal nmn and cbc is normal too... but ung ubo nya is hndi nawawala anyone here had the same experience???