Brief Answer:
Might be due to forceful muscle contractions

Detailed Answer:
Hi,

You might be indulging in rough masturbation or sexual intercourse leading to ejaculation. This can cause strong muscle contractions and ligament stretching involving groups of muscles attaching the hip with knee. The forceful contractions of these muscles and ligaments can result in mild knee pain. Any history of hip or knee injury in the past may have significance. It is suggested that you participate in a slower and less forceful sex or masturbation. If the pain persists then you should consult an orthopedician and get clinically examined for your complaints.

Paracetamol is a mild analgesic which is taken orally. An ointment containing pain killer and muscle relaxants may give better relief when applied on the painful areas.

Please feel free to correct any oversight in my interpretation of your problems and discuss them in detail as per your requirements.

Hope your query is answered.
Do write back if you have any doubts.

Regards,
Dr.Vivek

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