The Tragus often gets sore from the use of earbuds (because they are held in place by the Tragus). However, the Tragus can also be sore and tender from sleeping on that side of your head for long periods of time (if you don't move much during your sleep). Also, the beginning of a sebaceous cysts could be the cause of the soreness also. Although it may never materialize into a full blown cyst, it can still cause soreness until it resolves itself. This area (Tragus and earlobes) is often a common site for these types of cysts.
You can place some warm moist heat on the Tragus for a few days and see if this helps. If a cysts does materialize, you may need to have it excised and drained by your Physician.
Hope this helps!
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