If you’re an athlete, or even a weekender, or even an around-the-house piddler, and you incur a new or recurrent ache or pain, you might dismiss it for a few hours….but then get concerned when you try to get back into whatever it is you have to do. The ache or pain increases, or simply does not subside, and you start thinking maybe you should see a doctor. As this article points out, quoting doctors, this may not be a good idea. besides the fact it’s going to cost you time and money – and getting a red flag for your future insurer to tag you with – some of these may simply go away with that time-honored time-related thing called “relative rest.” What is relative rest? it’s that which takes you away from what it is that is causing the pain but not from other, generally less intense, activities. so, if your 
knees hurt from jogging these past few beautiful spring days, maybe you simply did too much too soon – the usual script. All you may need to do is take a bike ride or walk on a treadmill instead of pound the pavement. If the knees still hurt by the end of the week, you could conclude that running’s not good for you…or that you just jumped into it too fast….or your shoes, the ones you wore last fall, need to be replaced. HOWEVER, if the knee is keeping you from doing ADLs – your activities of daily living, like sitting at a desk or walking down the corridor.
If it’s causing swelling or weakness or instability, then go to your sports med doc ASAP. This article gives you some insight as to how to make the determinations, and why, but I can tell you this from my experience: most docs, esp general practitioners, don’t know much about sports injuries and will generally prescribe a pain killer, anti-inflammatory, and rest. The pain killer is often overkill; the anti-inflammatory is sometimes counterproductive to the healing process, and rest is, well, rest is something you can do for yourself, so give it a try: http://www.nytimes.com/2010/04/01/fashion/01best.html?ref=nutrition