If in the U.K., could you pay to see an experienced msk physio privately to get assessed and a rehab programme? NHS waits are long and treatment is generally very hands off, if not virtual due to Covid.
U.K. GPs really aren’t very expert about more severe musculoskeletal injuries. An experienced msk physio is a much better bet as they are specialised and see lots of cases. They can assess your knee and all your muscles thoroughly. There’s probably swelling and tightness in the quads, hamstrings, calves for starters
Exercising in water is very worthwhile too if you can access a pool.
Definitely see a physio, an appointment is usually. If you happen to have private healthcare through work, even better. Around £50-70 Self pay
Good luck