Let me just say that I LOVE SEINFELD!!!! its my favorite show in the whole entire world!!!!
Now that I got that enthusiasm out of the way, I am 20 years old and I live with my parents still, my mom always buys junk food..I have tons of it in the house so I can relate to how you feel. But you are only 14 so its much harder for you to do anything about it. I could drive to the store and get what I need (i'm a vegetarian and a health-nut so I eat pretty well).
What you need to do is not eat after 8 O'clock. It seems to me that you exercise pretty well which is great!. As for the food, ask your mom if when she goes to the store, to pick you up stuff (whatever you like that is healthy... fruits, Veggies, fish...etc.). Try to explain to her that you lost all that weight and you would really like to keep it off and start eating right for your own well-being.
From a Vegetarians point-of-view...i'd say cut back on the red meat (its really unhealthy for you). Have you ever noticed that Americans are the most obese? You could attribute this to all the meat-eating that is done here. Just a FYI....
Good luck! Try to say at your dads more often