I Am A Healthy 68 Year Old Female, Very Active

I am a healthy 68 year old female, very active in running, hiking, biking, kayaking, etc. I am experiencing a fairly strong pain in my left buttox when I sit for 10 min. or so -- and I haven't had it prior to the past few weeks. I've had no falls or injuries. Any ideas? It's pretty painful. Thank you.
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