Hi welcome to HCM.
Popping sound after trauma is one of symptom suggestive of significant trauma to knee. Bump seen on knee is most likely a joint effusion
. Pain is severe as there is high chance of internal injury
like meniscal or ligament tear.
You need to consult board certified orthopaedician for examination, if needed please go for MRI
KNEE investigation. It is best modality for knee pathology.
Hope I have answered your query.