Hi
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It is difficult to comment without examination. Lump behind the ear could be an abscess, folliculitis (hair follicle infection), lipoma (localized collection of fat), a cyst, an inflamed lymph node or a neurofibroma (localized harmless swelling in of nerve and connective tissue). You may not have been sick but local infections like dandruff or a dermatitis too can cause a lymph node to swell and be tender.
Consult your PCP and get this evaluated.
Hope this helps. Please let me know if there is any thing else and do keep me posted. Take care!
That happened to me (at least it sounds similar) last year but it went away after a few weeks. I think it was a collection of skin oils like a bad pimple in a weird place. However, if it's still there after a couple of weeks or if it gets bigger...I'd go to a dermatologist or even a regular MD. I sympathize...I freak bigtime if I don't know what's going on with my body. But chances are it's nothing, or if it's found so early, it should be easy to fix.
Yes, it could be a cyst, bug bite, or even a form of pimple. If it does not leave or gets bigger, I would see a dermatologist and have him/her look at it.