Left knee pain

Rodders30

After a while it feels like my knee cap wants to pop out. Today at about 55 miles it was quite painful on the downward push up hills. Basic bike fit hasnt helped. So not sure whats causing it. Dodgy cartlidge? Been over weight for many years so this hasnt helped. Right knee is perfect.

Dunno what to do, go to doctors, wear a support, suck it up?

Any advice appreciated.