At your age, nutrition is critical as you're still growing/maturing. Trying to lose 2 lbs a week will be difficult while maintaining a good nutritional balance.
Revise your goals to a pound a week, it will be easier and better for you.
Remember, weight loss/maintenance is a life-long pursuit.
You need to learn eating and exercise habits that keep the weight off rather than losing weight and then going back to the lifestyle that put on the pounds in the first place.
Talk to the track coach at your school, if you've got a good one, he/she may be willing to let you join the team even this far into the season or can at least offer some advice.
Being a part of the team can help with motivation. Don't worry about your athleticism(or lack of it
), a good coach wants to see each athlete achieve their best, not just focus on the studs/studdettes.
Also, some cross country programs( most likely the same coach as track) will have a summer training program.