recently i started jogging, not too much, just 10m a day at a moderate-fast pace.
I'm not unfit, i can walk for AGES (as in a few hours) at a very fast pace and not get puffed out, and i'm OK
my first few days jogging I was ok, but 3 days ago i got a stitch. I put it down to eating too much before (which i did). The day before yesterday I went on a run an hour after breakfast and got one in my lower tummy (rather than my ribs). I put that down to going after breakfast. However, yesterday I didn't eat much before and i got an even worse stitch (in my ribs). And today when I was doing my paper run (moderate pace walking w/ a backpack, for about 15 minutes. I have been doing it for nearly 3 years and have never had any problems whatsoever) i got a really bad stitch in my ribs.

How come?
Is it even a stitch? It feels like one.
Could I have somehow pulled an intercostal muscle (the muscles between your ribs)?

How do you stretch them out again?

(sorry this q is so long :P)