Hi.. Thanks for the query.. Itching at the back of mouth and upper part of throat can be due to allergic reaction to any foods.. It can also be due to environmental irritants like pollen, dust, animal danders etc.. So first of all you should consult an Emergency room and get your mouth and throat examined.. If there are no signs of infection then you can take anti allergics like Benadryl or Levocetrizine for reducing the itching and irritation.. Also gargle with benadryl solution or a steroid containing mouthwash. You can also do warm saline gargles.. If the mouth is dry then chew sugarfree chewing gums. Drink plenty of water.. If the symptoms continue to recur get an allergy test done for further confirmation of the cause and management can be planned accordingly.. Hope this helps.. Regards..