Feeling some joint pain?

Joint pain can be arthritis, tendon or ligament issues as well. A doctor can help better localize the pain. Try ice to your knee(s) for 20 minute or so after you run but if it persists you should have a doctor check it out.
Also are your shoes ok? Updating running/walking shoes can really help.

I've suffered joint pain since I was about 15 years old, and I've been relatively thin. It's not always weight related. Strengthening the muscles around the joints can help. Be careful about using NSAIDs (Ibuprofen, Naproxen, etc) because if used for more than the directed amount of time, it can result in liver damage.
Also, the pain could be posture related. I have hyperextended knees that I've found tend to cause pain when I stand with them in a hyperextended position for more than a couple minutes. Make sure your body is properly aligned so that it is being properly supported and not causing unnecessary strain to your joints (ie, back, hips, knees, neck).

Proper alignment consists of standing with your knees (not hyperextended haha) positioned below your hips and above the ankles, shoulders over hips, and your ears should be over your shoulders, rather than when tilting your head forward too much or backward. Be sure to utilize your core muscles in maintaining back support and don't stand with your back "jack-knifed" so that it curves awkwardly. That can lead to pain in your spine (which is really not pleasant ><).

I hope that this helps. I also recommend having a blood test (if the pain is persistent and gets worse) to see if there is any rheumatism present. It's always better to be safe than sorry, especially in matters of health. Your chances of healing and feeling better are that much greater when you catch and address symptoms earlier on.
Also, if you can't get to a doctor soon, purchase stabilizing bandages (Ace bandages and braces). I've found them to be useful on days when I'm in a particularly bad amount of pain.
There's also supplements you could take, though they're not always guaranteed to work. I was on a glucosamine chondroitin supplement for awhile that seemed to help, but only after taking it for a couple of weeks.
Another thing, just generally being hydrated can be beneficial. It keeps your joints lubricated and operating smoothly.

I hope you find a good healthy solution and that your joints feel better soon! : )

You can also have joint and muscle pain from eating foods you're allergic or intolerant to believe it or not. Gluten and grain allergies are very common for this. If you do suspect a food issue just remove it from your diet for several weeks and then carefully begin adding it back in and see how you feel. It will take a couple of weeks (or more depending on how bad you are) to get it fully out of your system. Just another thing to consider.