I've been returning to running from injury and been using walk/run technique. I've been plagued with stitches as well, which I used to suffer with a lot when I first started running. I find that if I slow down they do ease also try modifying your breathing technique. Some people recommend raising your arms like an aeroplane.
I only took up running a couple of months ago and also get stitches - i found that if you can, alternate the feet you are stepping with when you breathe in (ie breathe in for two paces and out for three) - the altenate stepping thing changes which side has the most downward force on it and so helps prevent stitches (which are almost always side-specific) in some cases - works for me. Slowing down, but not stopping entirely and massaging/applying pressure just below the rib cage on the side thats stitched also seems to help - though I'm not a doctor so don't know if this is recommended!
I used to use them when i was in the Air Cadets years ago hiking etc.. was tempted to get one for running, but wasnt sure what good it would do me (it holds 3 litres so thats an extra 3kg hanging from ya back).