It sounds to me like you are eating too high a proportion of carbohydrates. Rice is nutritious but it is a carbohydrate and as such it can pack on the kilos easily if you eat too many and don't burn them off.
Try to increase the protein portion of your diet. For example, rather than rice at breakfast, perhaps have an egg and milk dish, then a piece of fruit or some vegetables at breakfast.
At every meal, reduce your rice portion and replace it with a larger portion of vegetables. Make sure you include lovely beans and legumes, like chick peas and lentils. Also include a small serving of nuts every day. This is very important, especially for a vegetarian like yourself, as they contain some oils essential for the body, that otherwise are only found in animal products.
All the best!