Maybe you are bloated? I know my belly looks big when I eat sugar.
Not to scare you but this happened to my cousin. She was sent home from the doctors being told to do sit ups/crunches. Long story short during her annual GYN apt. the doctor felt something "not right" and sent her for a scan. There was a tumor attached to one ovary, going behind the uterus and attached the other ovary. Full hysterectomy, chemo and radiation later she is alive and well. But don't overlook anything medically caused. Always rule that out first. If all is well than I would blame stress as that has been attributed to belly fat retention. Hope all goes well!
Get an abdominal and lower abdominal scan done and rule out any medical anomalies. If you are having lot of fat deposit then start regular cardio activities such as running, jogging and swimming regularly for 1 hour. You should prepare a proper diet chart after discussing with a dietician and follow it strictly.
You should also remember that the fat which you have put the last is the first you will lose with cardio, so best of luck!