It's not the fact it was specifically bread, it's the fact I highly doubt you're supposed to have bread or anything more than maybe liquids or mushies at only 13 days post op.
Btw, chewing food to mush does not count. If it's not the consistency of baby food before it hits your mouth then it's not considered mushy food post diet acceptable.
Your stomach has been manipulated and sutured. It's wounded and needs time to heal. It's no wonder you're having this problem because you're not giving that swelling time to resolve itself.
Get back on your post op diet, follow it strictly, and tell your doctor exactly what you did and the result after. Let him make sure you didn't do any damage.
Best wishes.