What Causes Inflammation And Swelling Above Eyebrow After A Mosquito Bite?

my son got a mosquitio bite 2 days ago. it was rather large and red at first right above his eyebrow (he seems to react badly) but by end of the next day it was quite swollen . I gave him benedryl. This morning it is still just as large. It isn't that red just puffy and doesn't hurt him. Is this normal?