Quoting ☮Hippie Jesus☮:" Oh, I know... I was just trying to express how bizarre it is to me that this has become a problem. I ... [snip!] ... is how our son got it... from going over to his dad's and sleeping in the same bed as him, probably. Ughhh... What do I do?!"
Oh wow :( Idk. Is there a way you can make it so he doesn't go this weekend so your son doesn't get it again? Idk that's what I would do. I would either talk to his dad and tell him that your son just got over it and he shouldn't be around him until he is cleared of it. I'm sorry. I hope you figure something out. That would be awful to have to deal with it again.
ETA: Maybe his pedi can prescribe a preventative type medicine just in cas since he just got over it????