sandra has given some great advice jojo
make sure you drink loads of water, do exercise (and try and get some variety happening there) and eat regularly. NEVER skip breakfast. make sure you get adequate calcium and iron into your diet too
if you are worried though, it might be worth seeing your local GP for some blood tests - theres a few conditions that can cause a slow metabolism, and while its not likely you necessarily have one, it can be good just to get it checked out. for example if you have an underactive thyroid, it can be picked up on a simple blood test and cured with regular tablets... so worth knowing about!