I'm sorry, I really don't know. My stoma didn't swell in the summer, but I live in a country where hot summers are a joke. If it started after you went back to work, maybe it's also related to sitting for hours at at a time as well as the heat. All I can suggest is getting in touch with your stoma nurse or surgeon and asking what they think.
Dx Crohn's in summer of 2000. (Yay )
Tried and failed: 5-ASAs, azathioprine, 6MP, Remicade, methotrexate, Humira, various diets.
Had surgery Feb '13 - subtotal colectomy with end ileostomy. First thing to put me into remission in 13 years.
Had second surgery 10th July '15 to reverse the stoma and connect the ileum to the rectum. Feeling rough.