Hi - and congrats on getting started! I found I had a stitch the first week, too (and the first day of week two), but as I built my stamina, it seems to have subsided. I found it helped to walk longer if I needed to - in fact, I've been stretching the whole program to suit me, so I do about five days of each 'week' of the program, if you see what I mean.
Also - I am FAR from an expert (or even a runner!
) but make sure you don't push yourself to 'run' too hard or too fast - the program seems to be about building strength and stamina, so let your body take its time.
Stick with it!
Heather