Why cant i extend my knee (injury)?

I injured my knee 11 days ago on Nov 16 2010 playin basketball. i came down on and planted my left foot on the ground and tried to suddenly change direction slighty to the right, but before i could plant the next step i felt a sudden and sharp pain in my left knee. it was extremely painful. i didnt hear any pop though. it felt like i had brought all my weight down on my left knee and somethin just got strained or perhaps my meniscus got tore. i fell down right away with a lot of pain. im 25 and have never sustained a serious knee injury like this. immediately i could not straighten my left knee to lock it out so i had a bent leg while i was in pain. i got up and hopped on my right leg and could not bare any weight on my left leg cuz it felt so painful and tender/swollen inside the knee and was even shakin. i went to the ER the same day right after and they told me i sprained my knee. i feel the Physician istant told me this cuz i was able to stand on it and do a squat and take a couple of steps foward while squatting (but with difficulty and some pain and favoring the right leg for weight bearing) and cuz i did not have pain on the outside of my knee while he was touching it. the pain was and still is on the inside of my knee. i couldnt extend or bend it all the way cuz of pain. i had to use crutches for about 3-4 days because i could not bare weight. when i slept i had to turn my knee facing out because i felt pressure and pain if i turned my knee and leg in facing straight. after that i started to walk without crutches but very carefully at first and always with a limp and i had to watch my step very carefully cuz twisting caused a sharp pain and at first my foot and leg was still favoring a position turned outward to relieve pain on my knee while i walked. its day 11 and i cannot still fully extend my leg because it wont allow me to lock it out and i feel pain and pressure on the inside center of my knee when i try. my knee still looks swollen. i also cannot fully bend my knee all the way because i feel stiffness and some pain but the extending is a worse problem. i am still walkin with a limp but i am now able to turn my leg and foot in and keep them straight, but i always have to keep my knee bent even when i walk and this causes me to put strain on other leg muscles and my feet and left calf get really sore and fatigued especially. but i can move around a little faster now and can put more weight on my left leg and can turn and twist better although im stil very careful and dont try to make sudden twisting movements or high impact powerful fast movements because i feel i will hurt it. i dont try to run or even jog, just slow walking. i returned to work and its my 3rd day back and at work i have to stand and walk around all day. this is where my legs fatigue badly. the first day back i was limping badly and became slower with more pain as the day progressed. i also have to lift moderately heavy to very heavy stuff occasionally. im wondering what my injury could be. im very concerned that my knee still has not improved any in being able to extend out fully, its my biggest concern. im also concerned about the swellin because it has not gone down although its not extreme. i take pain pills occasionally mostly for work. i ice it occasionally, the first few day mostly, and i wear just an elastic wrap bandage on it. should i continue working and putting this kind of stress on my knee from all the walking and limping when im still having these problems with my knee. i saw another doc 6 days later on Mon Nov 22 2011 and she was tellin me the same thing that the ER told me, but after she played around with my knee a little (no pain to the touch on the outside) she hinted that it could be a tore ligament so she asked me if i wanted her to order an MRI and i said yes, that's what i was trying to get but its been hell cuz im on medicaid (public medical insurance for low income) and there are long wait times for doctor appointments and i cannot go to a specialist until the regular doc that i saw approves it. and the doc walked out and i did not see her after that. so the nurse comes in to tell me i was done and that i would get the MRI info in the mail. im still waiting and i dont know what for. i dont know how this works if it will be covered or has to be preapproved. it sucks to not have good medical coverage. i am still slow and careful on my knee especially when i have to climb and go down stairs and im still afraid to twist it fast. not being able to lock it out still is more worrisome to me. what could it be? has anyone had the same symptoms as me/ same experience? please share and what was the outcome/ treatment? can it be healed on its own with time back to normal to 100% again so that ill gain my full extension and flexibility and be able to lock it out again? please help