HI,
    I understand your concern.
    A bout of 
dry cough is definitely very troublesome.
    Dry cough can be allergic or infective( bacterial or viral ) in origin
    exposure to allergen ( dust, pollen, fumes).. irritate throat & cause dry cough.  This can be controlled by anti 
allergic cough syrup like Benadril syrup.
        Viral cold followed by cough is common. Starts with 
common cold, 
fever & fever. Other symptoms go in 5 days but cough takes long .. it needs cough supressant syrup .
      Infective ( bacterial)cough is dry to start with.. & starts producing sputum later. Here antibiotics are needed along with cough expectorant.
    * In 
pregnancy you should consult a physician before taking medicines. After physical examinations & advise for investigations, you will bw prescribed medicines with other medicines ( antibiotic, anti allergic, bronchodialators .. as per need) along with cough syrup of specific type.
   * along with the medicines you have to-
     - avoid allergens,/ cold drinks, sour food
     -hot saline gargles,
     - drink plenty of warm water
   Thanks.