Why am i hungry al the time?

ok i am 15 and i am a little chubby I have bin my whole life but i exercise quit a bit and am starting to loose wight.I wanted to raise my mitabilism so i started drinking green tea and i think it has helped a little bit.But i seam to go through cycles wear i am just not hungry and might only eat 1 to 2 meals a day and not because i am starving myself just becasue i am not hungry.Then there are times were its like i am hungry all the time why is this and what should i do.