Dermal Fillers 4 Months Ago: Why Does my Face Look Swollen Every Now and Then?

i had dermal fillers about 4 months ago. But why does my face look swollen every now and then? One day it's not that swollen and in the next day it looks swollen,. people around me always notice and asks me what happened to my face if I have allergies or what? I'm just wondering why sometimes my face is not that swollen but many times it looks swollen? I don't understand. Thank you.