Reaction to chemicals used during Jewelry repair - HELP

I own a 14k gold necklace. My grandpa used to sell jewelry and gave it to me over 10 years ago. I've had it all this time and never had any issues with it. One small part on it fell off, I let my dad know and he said he could take it to a repair shop for me. On Wednesday 12/6/23 he took it to a repair shop, He brought it back to me that same day. Yesterday 12/7/23 I put on the necklace with the pendant before I left for work and had it on all day. After about 15 minutes of wearing it, I felt my neck starting to get itchy, I didn't think anything of it at first. But then it persisted throughout the whole day so I figured it might be the necklace.

I woke up this morning to red blotches all around my neck where the necklace was. The skin is damaged and almost looks like it's eating itself in some areas. I am terrified, does anyone know what chemicals they use during the repair process, what this possibly could be from, and how to fix it?

I tried setting up an appt with a doctor but no one is available and I have to wait till Monday for a call.