What you have could be a condition called as angioedema. It is basically an increased skin sensitivity response . It happens because of various triggers and the trigger is most often different for different people. With angioedema normally both eyes get involved and in some cases patient can also have difficulty breathing due to the involvement of the vocal cords . The other possibility is that of an insect bite reaction if you only have it in one eye. Also, it could also be a manifestation of drug reaction which could also happen just involving one eye. A thorough Examination and detailed history evaluation would help to accurately make a diagnosis. For you can take tablet levocetrizine 5 mg to subside the itching. Hope this was Helpful.