Well if you are excercising you should eat more than a packet of crisps. Crisps arent the healthyest option either. They are ok once and a while but try to have a balenced diet. Swap the crisps for a smoothie. It's way healthier and in my opinion it tastes way better. The link below is for some smoothie recipes you could try ^_^

http://www.smoothieweb.com/

Make sure your diet is balenced. It's ok to have something sweet or oily once and a while but generally try to stick to healthy stuff.

As for excercise of course it's good and if you enjoy it keep it up but don't push yourself. Whats your BMI? I'm sure your not fat at all and don't need to loose weight. If that is so you only really need to do excercise to keep yourself toned and fit and for the fun of it :) Cheak your BMI on this link.

http://www.nhlbisupport.com/bmi/

If you feel dizzy while excercising it's a sign that you need to take a breather.

Do you have low blood pressure this is another reason for dizzyness.

You aren't ugly nobody is. Beauty is in the eye of the beholder and the confident ones who smile and stand up straight look pretttyest. You are beautiful and its your job to believe it :) xx

just make sure you are eating right. Eat yout veggies, fruits, protein, and diary, thats all you need to stay healthy eating wise. And its ok to have some junk food one awhile, like maybe even once a day, just not something really big. Excercising is good, just make sure you dont do too much, your body needs a break. for a teen you only need to work out like 4 times a week, for a hour.
If you are dizzy and tired, that means your body needs a break, so just relax.
You should be eating more than just a packet of crisps... thats in no way healthy.
And most of all just be comfortable with yourself, and be healthy without going overboard.