SKY,
If you have dislocated your knee and are in severe pain you should call your Dr. or present to the ER. From your description of the popping sound, and severe pain it feels to me like you have a ligament injury, most likely an ACL. However, with your complicated history from your accident I would try to get in touch with a medical professional.
If swelling comes up immediately or within the first 48hours, it usually indicates a ligament or cartilage injury. If you have a knee ice wrap that provides compression now would be the time to be using cold on your knee.
I am pretty sure you know more than I do on how to treat your injury.
I am sorry this happened to you and I will be waiting to hear how you are doing.
Kindly,
Kitt