Pateller Tendinitis is an injury to the patella tendon that connects the kneecap to the shinbone. The patella tendon works along with the quadricep and other thigh muscles to help extend the knee forward during running, jumping, and transitioning directions. So if the pain you are experiencing tends to get worse during or after your runs, then it very well might be pateller tendinitis (which is also commonly referred to as "runner's knee") among the running community. But you might also feel it flare up the most when you are jumping, and it could still be pateller tendinitis.
The most common sympton of pateller tendinitis and runner's knee, aside from the pain that is focused between the kneecap and where the tendon attaches to your tibia, is swelling around the knee cap and patella tendon. Over time, if left untreated, the pain will start to get worse and become debilitating so that even every day tasks and chores (like climbing the stairs or just accomplishing mundane, routine tasks) become painful.
The pain is caused by tiny tears in the patella tendon. If left untreated, these tiny tears start tearing more and result in more pain and stress placed on the knee. Runner's knee can be a catch 22 to heal from because it is usually caused by overuse. Yet, it also continues to get worse from overuse, so it is absolutely imperative that you take some time off your running to heal.
To help decrease these symptoms, if you start to feel your pain worsening, the best thing you can do is rest. Take a few days to a few weeks off from your standard exercise routine. The knee needs rest to help the inflammation go down, which is part of the reason you are experiencing pain. You should also be taking pain killers, and icing and elevating your knees twice a day (ice for 20 minutes). If after adequate rest, icing the area, and taking pain medicine fails to relieve the pain, it is time to see a doctor about your condition.