I've had multiple knee injuries and a couple of surgeries. Here's what I can say.
Odds are that you don't know when you did it, but something happened and it has gradually gotten worse. If it is a miniscus, it is more of an "uncomfortable dull pain" that doesn't subside. In this case, icing is not going to help you much, if at all. Icing only helps reduce swelling in ligaments/tendons/muscles. The miniscus is an interior cushion. It is most often injured by a verticle impact...not rotation torque. If you planted really hard on the concrete, with a lot of force straight down, you could have torn a miniscus. My guess is that this was done via the torque which means that it is either the ACL/MCL or sometimes the Patellar Tendon. If you feel any instability, like your knee sliding around abnormally, it is the ACL or MCL. A sprain of the MCL is no big deal...just some physical therapy and rest for about 5-6 weeks. An ACL sprain is likely going to require surgery. If it is only partially torn, then you may not have to have surgery now, but you're essentially a ticking time bomb.
The problem with knee injuries is that none of the knee ligaments or miniscus regenerate. Once they're torn, they're torn and surgery is the only remedy. I've had ACL reconstruction (from a softball injury) as well as a few "scopes".
It could also be some torn cartilage floating around causing the pain, but this is usually an issue that arises years after the initial injury.
In short, go to the doc...get an MRI...and hope for an MCL sprain. I knew my knee wasn't well, but I could walk around just fine before I found out I had torn my ACL. Sometimes the injury is much worse than it seems.