What caused it?

I'd go to CVS and get one of those neoprene and velcro braces until you go to a doctor, or it strengthens. Maybe pick up a cane if it's that bad.

Thing about those ligament injuries is the injury happens, knee gives out, tough it out, pain/swelling goes away, then 6 months later it does it again, out of the blue. Another 3 months goes by, and boom, repeat again. Just keeps getting more frequent. If you have a Jag, you probably got health insurance, so you might as well have it looked at.

Should be outpatient surgery, weekend on the couch (hooked up to a little pain pump) couple weeks of crutches, couple weeks of therapy. That is how it went for a guy I know that had a partial tear on the MCL. I think it was 2 months of disability for him. So much going on in the knee, the process varies alot.