I have sneezing fits like 4-5 times after eating sweets things like jam with bread,desserts!etc.i have turbinate hypertrophy.is this allergy to sweet?

Unlikely: If you are referring to sugar, then there is no known mechanism or scientific basis for developing an allergy to it. However it is possible that you may be allergic to one of the ingredients in "sweets" such as dairy, egg , wheat , fruits, etc. Allergic diseases often cause nasal congestion and thus this may be the cause for your turbinate hypertrophy.