hi Christie... is it the stoma that's swollen or the skin around the base of the stoma?
if it's the actual stoma, it could be that the appliance you had on before you changed it wasn't fitting properly, and the apperture was sitting on the stoma rather than around it's base... or it could be something that needs showing to your doctor if this isn't the cause..
if it's the skin, then that's quite common if it has become sore from the output leaking just inside the apperture. if the skin's swollen, but not sore, again i'd show a doctor asap.