Hello As you mentioned that zyrtec causes some relief but not now . You get some relief with steam inhalation i.e. steam causes dilation of bronchi hence relief. When patient come in contact with some allergen as ( mite , dust , hay , mold, sudden fall & rise of temperature , humidity , fine dusting powder) he develops bronchoconstriction ,hence cough ( very severe as may be in your case) . Same thing is happening in your case but codeine , methylprednisolone and antibiotics are not effective i.e. severe allergy . When such type of patient visit I usually prescribe them to take monteleukast+ bambuterole ( tablet ) once or twice in day depending upon the nature of disease and severity of disease . You can take till complete relief. 2nd reason of such sever cough may be some foreign particle inhaled in airways and cause sever cough ,but in your case cough may be due to allergy .Hope this information will help you.