What have i done to my left knee?!

What have i done to my left knee?

I have been having this issue with my left knee for ages now and I don't want to bother the doctor with it every so often when i stand or walk my knee pops and it gets very sore also if i sit in one position for too long my knee stiffens up and i can't bend it properly i've also experienced my knee buckling under me when i try to run is it because i greenstick fractured my left leg when i was a very young child or is it because i did ballet for 7 years then stopped suddenly?

2 weeks ago
the main reason i don't want to see my doctor is because i have learning difficulties and doctors don't take me seriously

2 weeks ago
I also forgot to mention that i fell flat on my face in 2000 while walking up a steep hill I fell because i didn't see the speed bump. i insisted on going to the hospital near the college when we came out of the interview they told me it was just tissue damage and put a tubi grip on it

YOU MAY HAVE A TEAR IN YOUR KNEE, SO YOU DEFINITELY WANT TO SEE A SPECIALIST. YOU MAY NEED A SURGERY AND THE WORST PART IS KNEES NEVER HEAL. THEY'RE A LIFETIME INJURY. SO GET IT CHECKED YOU YOU RISK WORSENING THE CONDITION.