Quote from AAAintheBeltway:
Did the pain begin with the new shoes? If so, that could be the issue. For me, shoes usually cause achilles issues though, not knee.
Knee pain behind the kneecap is typically runner's knee, an overuse injury. Rx is to cut back. Knee pain can also be from arthritis. Symptoms can include pain when using stairs, swelling, sore in the morning. Not much yu can do about it, but you need to do everything you can to strengthen the joint area, eg do leg extensions. Knee pain can also come from a cartlege tear, which is serious and requires attention from an orthopedist.
Considering that apparently it happened after this big stress on the knee I would rather consider a stretched ligament. It could also be the meniscus, depending on where the pain is.
If it doesn't go away in a few weeks, worst in a couple of months, I would talk to a doctor. In the worst case surgery might be necessary.
