I recently became a vegetarian? Please Help!!?

6 months ago i became a vegetarian and in the past couple days I have lost 3 lbs. You may think, it is only 3 lbs, but I am 13 and I am a slow grower. I have not been excessively excersising, and I am eating the same foods as usual. My mom says I am not getting enough protein, and this is the reason I have lost weight. I think I eat enough, but what i am worried about is other nutrients I might need that come from meat. What do I need to eat to make sure I stay healthy and how much protein do you need in a day? What are the health benefits of being a vegetarian? Thanks!!