I am 5'5 and weigh 276 pounds...am i overweight?

Yes: You are obese for age. If you want to change this find a dietitian to work with to help you with a sensible diet and exercise plan. Weight watchers is another good resource and often will accommodate older teens.

Unfortunately, yes.: Your weight and height puts your body mass index at 45.9, which puts you clearly in the obese category. You need to lose weight. By the BMI, although it's not a perfect index by itself, your weight for that height should be around 150 at the most.