Knee Tendonitis Help

Background: I've had knee problems for the past 4 years. Four (almost five) years ago I knocked my kneecap out of place almost an inch; after extensive therapy my knee was healed. Then, I hit it very hard against the side of the bath tub and it started to hurt again. I had an x ray and MRI done that showed my patella was fraying, cartilage was torn, and I had a lot of fluid stored in my knee. I had arthiscopic surgery two Christmases ago and my surgeon found nothing wrong except for a bad case of tendonitis. I have undergone four rounds of rehab, RICE therapy, blood stimulation therapy, and many ultrasounds to no avail or relief to my knee. (My grandmother has bad knees for different reasons and has received cortisone injections that made her injuries worse...I refuse to get the injections because I heard they don't help in the long run; I'm also prone to panic attacks if I come in contact with needles.)

Problem: My knee still hurts very bad and is sore to the touch. It sometimes turns red and bruises, without me falling or hurting it. I cannot run, walk, bike, sit for too long, kneel, or lift heavy objects, and it can be difficult to drive. Sometimes I will be walking without my knee hurting and it will crack very loud or it will crack and I will fall. My doctor recommended letting my knee heal on its own and that I would qualify for knee replacement surgery in my mid-late 30's (I'm 18 now). My parents seem to think this is a neurological problem or extensive nerve damage, whereas my doctor says otherwise. My parents refuse to believe that it's possible to have chronic tendonitis.

Question: My question is, is it normal for knees to crack loud? What kinds of knee tendonitis are there? Why does my knee keep brusing if I don't hurt it or hit it? Are there any doctors that specialize in tendonitis in California? Are there any treatments that can help my knee? What are my options for treatment? Do cortisone injections help the knee in the long run, or is it more short term relief? Is it semi-common for people to have tendonitis for two+ years?