Is my occasional facial swelling really a food allergy?

For about 6 months I've had occasional facial swelling.....my face will be fine for about a week, sometimes two weeks and then out of nowhere my face will start to look very puffy and basically swollen.....I've had no less than 3 blood tests in the past 6 months....blood work is always fine....because my symptoms come and go the drs. are pretty sure it's some sort of food allergy or delayed food reaction....whereas if it were a thyroid problem, my face would just remain swollen.....so...has anyone ever experienced anything similar to this....I have an appt. w/ an allergist next week,,,,thanks in advance.