TMI-penile swelling in 3 year old

My son is 3 and this has seem to become a reoccurring issue.

We took him to the ER several months ago and we figured it was a bug bite. He had several other bites in the pelvic area. But it KEEPS happening. This is probably like the 5th or 6th time and it is random.

I'm starting to think it is not bug bites doing this. We have an appt Monday and an urgent care appt today but I wanted to see if anyone has seen something like this before?

It doesnt affect his peeing and he says this one doesnt hurt. The first couple hurt.

They also go away on their own but occur super fast.

This is about the full side of his penus shaft.