It's very unusual that your temperature under your arm should be cooler than under the tongue. Normally that should be the other way around with the underarm temperature being approximately 1 degree cooler. When taking your temperature orally, make sure that you have not had either a cold or hot drink for at least half an hour before as that can affect the reading and make sure it's tucked well under the tongue and keep the mouth closed. If you are really concerned about measuring your temperature accurately, it might be worth getting one of those electronic thermometers that you point into the ear (like the ones they have in hospitals) which reads it almost instantly. Hope this helps.
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