Katy, as far as oregano oil is concerned, some people have taken as much as 20 drops a day, however I’m not in favor of that much for more than a few days straight and then backing off on the number of drops. Personally, I wouldn’t take more than 16 drops a day for more than a few days at a time. It wouldn’t be a bad idea for everyone who takes more than a few drops a day to be aware of overdose effects such as a tingling feeling inside the mouth, a rash or vomiting. These can also be signs of an adverse reaction to the oil. However many drops you end up taking, you’ll need to work up to it a drop or two at a time, waiting a few days at the very least before increasing the current dose. Oregano oil has been known to cause bad die-off reactions.
I’m afraid I have to say that I’ve never heard or studied anything concerning the ‘cold feeling’ you described, but I’ll do some research and see what I can find.