Knee pain post picking blackberries

I was squatting down picking blackberries last weekend and went to stand up and heard/felt a crunch which took my breath away. i initially couldnt put any weight on my left leg but after a couple of minutes i managed to put a little weigth on and it clicked loudly and felt fine.

i now have no discomfort when inactive, slight discomfort when walking and more severe if my knee twists and when walking up and down stairs, squatting, etc. the pain is in the outside of my knee, slightly towards the rear. the joint also feels different - a swollen type feeling but doesnt appear swolen visually.

i had DDH in the same leg which wasnt 'fixed' until i was a teenager, surgery left me with nerve damage and poor muscle function in my thigh. this and probably a large helping of bad habit left me reliant on my leg 'locking' straight (actually slightly hyper extended) for weight bearing (not entirely sure if physio would help with this as i cannot recall ever having any).

my knee now doesnt feel as stable, almost like it is hyperextending further and the back of my knee becomes quite tender if i do much walking. an nhs physio referral will take weeks and im not currently in a position to be able to pay for private treatment. i could really do with some advice on how best to support it so it can heal or so that i dont damage it more in the mean time.

thanks!