Hello Mini-mo. Thanks for your post and the description of your problem. I have never been overweight but I had a huge swelling of the belly area immediately after the operation and it took more than two years before it started to subside slightly. Even now, I have difficulty comprehending the reasons why I cannot seem to get the muscles back that I once had. Like you, it seems to affect the way the flanges won't stick evenly and that is why I made my own baseplates with two belts to hold it on. The top belt tends to be about 2-3 inches longer than the bottom one for a comfortable fit so you can imagine the difference in the circumference of my belly. The response from my stoma nurse was quite matter-of-fact in telling me that I had a hernia and that wearing a belt might help, at least to prevent it from getting worse. Although I looked 'fat', there was no insinuation that I was overweight. In fact, I had lost weight for the first time in my life and it was suggested that I try to bring my weight back to what it would normally be.
As for the pain. I did find that the hernia belt helped with this as it seemed to give support in the area which was most painful. My reasoning was, that the muscles had been weakened and were being stressed by the weight of whatever it would normally have supported. The belt just gave that extra support.
I hope you can find your own solution to these problems.
Best wishes
Bill