First, I'd check out the stones, metal, and anything else on the necklace. Scarabs aren't a symbol of illness, at least not in ancient Egypt (which is probably what it is meant to mimic/be). It's possibly a cheap knock off that had some sort of transfer to it, but more likely than not it was a coincidence. I'd clear my mind about it being interrelated, clean it up really well (after checking about the materials it's made of), and wear it for a bit. If you keep getting sick, it's possible you are simply allergic to something in/of it.
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