So this post is ancient, but in case you still want to lose weight, I'm going to reply.
First, people shouldn't make you feel so bad about yourself if you're trying to lose weight. The first thing you need to do is love yourself, or at least like yourself. If you continue to let other people bring you down, if you do even get to an ideal weight, it will never be enough. Trust me, I've been there. If you don't love the person you are right now, then you will either not lose any weight and be so depressed and disapointed OR you will lose tons of weight and never think you're good enough.
Second, I would say that you're in a tough situation with your parents not supporting you. My mom was always telling me that I was beautiful the way I was, but she still supported my weight loss journey. Idealy, I would like you to find a friend or a teacher or anyone that you can talk to who will support you and keep you on track. If you can't find anyone in real life, turn to the internet and find people either in similar situations or that have been where you are now and were successful.
Third, nutrition is key. You hear that all the time, but it's true. Google an online BMI calculator and a calorie calculator to see where you are, where you need to be and how many calories a day you should be consuming. Also, I suggest toning down the amount of sugars and sweets you eat. Don't cut them out completely because your body will go into withdrawl and you'll want them so bad and that sucks. Always keep tabs on your proportions. Never eat a steak without greens to go along with it; never eat starches without lean meats and veggies. Things like that. Now, I personally wrote down eveything I ate and how many calories each thing was. Then I would add at the end of the day and make sure that I was within my calorie range. Also, I didn't eat after 7 and I drank TONS of water, which the water is essential. And I don't mean water with Crystal Light or anything else you add to it. Just plain water. Ice water makes your insides cold and presumably makes your body work more which could potentially help you lose the weight.
As for working out, I found a site a while ago, which I hope is still there, that the subject is "How To Get A Bikini Body In Four Weeks" and it is FULL of excersizes you can do in your room! They all tone up your body and they're private so your parents can't tell you you can't work out! But don't expect a bikini body in 4 weeks... Losing weight takes time.
Anyway, I hope this helps someone. =) Good luck!