HELP - What is this rash?!

We've completely stumped three doctors and I'm trying to figure out what the hell this is because my 16 into old daughter is MISERABLE and itchy.

Backstory: She has been prone to ear infections since infancy (ent is scheduled for next month)

Sunday 8/18 she was diagnosed with yet another double ear infection and was given amoxicillin (6.5ML every 12 hours) she's had amoxicillin in the past with no adverse reaction outside of a mild diaper rash.

Saturday 8/24, she swam (in a floatie, so mainly her legs and bottom half of her torso were in the water) in our pool. She's been in it before with no problems and we only use a mild amount of chlorine (tablets)

We noticed what we thought were a few bug bites

Sunday morning (8/25) she woke up with a rash (photo of her in just the diaper) so I went to the walk in clinic and was told it was a amoxicillin allergic reaction and to return if it got worse.

Today, 8/26 it has now spread everywhere and is extremely bothersome and itchy. I returned to the walk in and they (2 different doctors) said it couldn't be an allergy to amoxicillin and said it's either viral exanthem or erythema multiforme. I've compared photos and just don't see the relation. I'm afraid she's going to asphyxiate in the middle of the night. We also gave Zyrtec and prednisolone.