Brief Answer:
Capsular inflammation likely.

Detailed Answer:
Hello,
Thanks for posting your query.
At your young age, the pain in the knee is more likely to be due to stress related minor capsular inflammation rather decrease in the joint lubricants.
The mild inflammation of the knee mostly subsides by taking antiinflammatory agents and mild pain killers like ibuprofen. In some cases for acute problem muscle relaxants like thiocolchicoside are needed after consulting with your orthopaedician.
If still there is no relief then oral steroids and oral lubricating agents like glucosamine sulfate and chondroitin are given. Injections - intra- articular are the last options to be considered if all the above measures fail.
In the meanwhile, for symptomatic relief:
1. Give enough rest to your knee- use a knee brace.
2. Take mild pain killers like acetaminophen or ibuprofen.
3. Stronger prescription NSAIDS with muscle relaxants may help if simple analgesics do not help.
4. Hot compresses to your knee will be useful relieving measure. You may apply a local analgesic gel on that area.
5. calf and hamstring stretches can be helpful under the guidance of a physiotherapist.
6. Generally we recommended, rest, graded exercises, rest and graded exercises to let you know the right amount of time you can spend on exercise without injuring yourself.

I hope this answers your query.
In case you have additional questions or doubts, you can forward them to me, and I shall be glad to help you out.
Wishing you good health.
Regards.
Dr. Praveen Tayal.
For future query, you can directly approach me through my profile URL http://bit.ly/Dr-Praveen-Tayal

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