I haven't heard of silk allergies.  But it could be something on the silk - perfumes, oil, manfacturer chemicals, detergents..  I was thinking bug bite also.  I guess all you can really do is see if it happens next time you wear the necklace. 

What is this Mecca cream?  It sounds interesting!

I also use cortisones for itches, but some people don't like that.  You can try Aveeno lotions because the colloidal oatmeal in it sooths itching.

But if it lasts longer than a week, I'd get it checked.  It sounds like you're doing much better though, so I'm glad!

Cynde