I had a knee operation 13 months ago?

I had a knee operation 13 months ago. Around 3 months ago I fell over a pallet in work and attended the hospital to get my knee checked but there was nothing found.
2 weeks ago I was on holiday and it suddenly gave in on me, leaving my knee popping and me in pain and my knee swelling. It reduced with a cold compression but after flying and doing normal activities it has swollen again and painful. Any ideas what this could be please?

Age: 25
Female
Medications: Asthma inhalers, eczema creams, epi pen

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