Whats wrong with my metabolism?

Okay so im an athlete and iv been doing athletics since i was 7 (im now 15) so iv always been quite thin and i have a really fast metabolism....but i was hanging out with a guy in school for a few weeks and i stopped eating as much. Now we dont really talk and i think my metabolism has slowed...i feel like im gaining wait....if i start eating the way i used to and keep up my training will my metabolism speed up???please help :/