I am constantly hungry?

I'm turning 17 this year I'm a female, I'm 156cm tall and weigh 45kg . I do afternoon jogs most days and have been on a vegetarian diet for a year and a half now. I constantly feel hungry, for instance an hour ago I ate 2 grilled sandwiches and I'm hungry again! It's only started recently though, I don't know what it is. I'm pretty healthy, drink loads of water during the day so I'm just not sure. I'm thinking I might see a dietitian or my doctor but thought I'd just see if anyone else has had something similar to this. Thanks!