I was vegetarian for about a year. It can be easy to gain weight on a vegetarian diet especially if you are still eating dairy and lots of carbs. Instead of eating more vegetables and fruit I went for the cheese and bread. If you are feeling hungry more often it is probably because you aren't getting enough protein and fiber in your new diet. Try to include black beans, oatmeal, almonds, low fat cottage cheese just a few suggestions that keep you fuller longer. I would recommend a daily multivitamin as well.
Hope some of this helps! Good Luck!