Your stoma will bulge out like that frequently. The base size of your stoma shouldn't change though and I hate to see someone cutting their flange too big because of it. If you need to cut it bigger to get it over the bulge, I hope you're using paste or Eakin seals around the base to fill in the gap.
It puffs in and out for many reasons; normal peristalsis (the movement in the intestines which moves your food), hydration, temperature, etc. It's nothing to worry about usually unless it's getting much, much bigger and staying that way which could be a prolapse.
If you have any questions, please post them with a new subject. People may not see your question if you put it in another, unrelated post. There's no stupid questions, so ask away.
49 years old, CD since I was a child.
Six resection surgeries, permanent ostomy, adverse reactions to Remicade, finally off of Prednisone, hoping for a long remission from this last surgery.