Hi, from the description you have given it seems you are having an eczematous lesion rather than cold sore. Cold sore is a viral infection where you get painful cluster of fluid filled blisters that has a tendency to recur at the same site. It occurs through a close contact with infected person and recurrences can be seen with fever, trauma, stress, hormonal changes during menstruation but as your lesion is itchy and exuding fluid it is most probably acute eczema. Take an oral anti histamine like cetirizine and apply a good antibiotic steroid cream twice in a day. Also keep the area moisturised. Hope that answers your query.