Have you been checked over by a doctor? A swollen tummy that feels hard should be investigated as it can be a sign of an obstructed or constricted bowel. (Although if you don't get any pain this is unlikely to be the case).
As you are a vegetarian your diet is likely to be quite high in fibre - this alone can account for bloating, especially after a pretty major bowel infection like cholera. That will have left your insides quite sensitive.
Try cutting down on insoluble fibre (bran, for example), and make sure you get plenty of protein. If that doesn't help, see a doctor if you haven't already done so.