Thank you for choosing DoctorSpring. I have discussed your concern with our team Rheumatologist.
I have gone through your symptoms which is predominantly related to the left knee. This is most likely something we call a "Monoarthritis". (Or inflammation of a single joint. ). Another possibility is non specific musculoskeletal inflammation around the knee. I am of the opinion this is more likely to be a mono arthritis.
Monoarthritis can be due to a number of causes ranging from infections to trauma. Crystal disease (Gout), urinary infection, osteoarthritis etc can also present like this. In your case the most likely cause in a trauma which could be from a minor injury , unaccustomed exertion, or trivial injury which you might not have noticed. This could have happened even few days back.
A confirmed diagnosis requires further tests like Xray of the knee, Physical examination and a joint aspirate study. BUT this is not necessary in all the cases. Since you do not have fever, pain, swelling you can judiciously observe how the pain evolves. There is high chance that it can spontaneously resolve. You can take an OTC anti inflammatory NSAID like Ibuprofen 400 mg twice daily for two days.
As of now there is nothing to worry. If the symptoms persists beyond 2-3 days and/or if there is pain , swelling , fever (which are suggestive of a condition called Septic Arthritis, which is a medical emergency) you should get medical help for further evaluation.
DO REST THE LEG. DO not exert.
Hope this helps
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