Could be a persistent milia is my guess. They can grow over time.

Treatment is usually a topical retinoid or an extraction from a dermatologist. But! Be careful. Yours is big and you don't want a scar if possible. So, probably best to see a dermatologist, but stay fiercely your own advocate. Tell them you want to try to avoid a scar and are willing to be patient. Maybe a topical could eliminate it still? I'm honestly not sure. But I would think that getting something that big extracted risks a scar. Anyway, be careful, be clear with your derm and don't go under the knife with anyone until you are 100% sure they are good and you feel totally comfortable with them.

I would push for at least an ultrasound wo see if theres anything going on. It could be a type of hyperplasia or milia, or even a resulting reaction from a bug bite.