The rib pain and stomach pain sound like a cramp. Cramps usually happen while you are running, not afterwards, but sometimes you might get one for a short time after you finish running. Was it a sharp pain and did it go away fairly quickly or more of a dull soreness that has continued for a day or so? Sharp and quick=cramp, dull and continuing means you've probably worked a muscle you haven't worked in a while. You do have to engage your core muscles when you run.
Also, the impact of running can sometimes cause odd pains. I broke my collarbone as a kid and sometimes when I run, the impact will make my collarbone ache a bit. But it stops when I stop running.
The impact is also hard on you back, especially your lower back. Make sure you stretch out well after you run so that your back doesn't get tight. If I don't stretch properly after I run, I can really feel it in my lower back.
The first time I ran, it felt like I was sore all over. I think my eyelids even hurt. I could barely move for days. But that went away pretty quickly once I started exercising regularly. I've never been that sore since.
My Before and After Pics
"Decide what you want; decide what you're willing to exchange for it; establish your priorities, and go to work." --H.L. Hunt
"Life has hills. Set the treadmill at an incline."