Usually in kids many lymph
nodes are normally palpable. They are firm and mobile.
Since you say it does not seem to move, it may not be a lymphnode.
And 5 months is too long for insect bite swellings to stay on.
I can very well understand your worries.
May be you can ask your pediatrician
if FNAC (Fine needle aspiration cytology) can be done from the swelling.
Don`t get paranoid, just go for another opinion if you need.
Hope you find my answer useful.