Dear friend, welcome to HCM> from your description , it seems to be a case of meniscal/ ligament injury
. (i.e. traumatised internal disc/ strings of the knee joint)
best way to deal with it is to see an orthopedic surgeon also doing knee endoscopies.
pl. avoid undue stress
on thet knee. and act on medical advice
hope you have no major injury and can do your gym wlll again.
pl. keep me posted ..