I have itchy throat and mouth. is this an allergic reaction?

Likely Yes: Itchy throat and mouth are very common symptoms when you are allergic to something. Most commonly- a food item such as fresh fruits or vegetables. Is it occurring all the time? Or just when you eat certain things? Also, do you have seasonal allergies? Seasonal allergies sometimes present that way as well- along with nasal congestion etc.

Itchy: Is it after eating fresh or raw fruits and veggies? It might be oral allergy syndrome if this is the case. Itchy mouth and throat can also just simply be due to allergic rhinitis.