Straining can cause a variety of problems, and it’s well worth the time and nuisance to find a way to avoid it. Pain in the side or back isn’t likely to be a hernia, but that doesn’t mean it isn’t an injury of some sort.
If your stool is solid then that’s likely to be a source of (or contributor to) the problem. J-poucher’s stool should be soft, with a texture something like pudding. It can be made softer by eliminating bowel slowers like Imodium, drinking more water, and/or using soluble fiber (like Psyllium or Citrucel) as good, simple steps.
If your stool is already soft then other causes have to be considered: strictures, sphincter issues, pouch prolapse, pouch malpositioning, and perhaps a few others. The exact cause needs to get figured out so an appropriate treatment can be devised. Until that’s resolved an alternate method of pouch emptying could be helpful, generally emptying the pouch through a catheter, sometimes with the contents loosened up with an enema.
You likely need a good gastroenterologist to help with this. Good luck!