About 4 Days Ago My Right Leg Became Very Painful

About 4 days ago my right leg became very painful from where it joins the trunk of my body to the knee in the front of the leg ONLY...not sides or back. I have not fallen and I do not have osteoporosis. I had partial hip replacement surgery on the other (left) leg in June. Could this be referred pain? I am bewildered by the occurrence and do know how to treat it...Bengay does relieve the pain somewhat. Thank you.
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I am 87 years old.