I am extremely saddened by my weight.what should i do?

im 18 years old and i am slightly overweight.the problem is that i cannot stick to a diet and exercise plan and each time i fall off the wagon,it takes me a week or more to get back on track.every time i mess up i regain the lost weight and i end up feeling extremely sad and depressed.this has been going on for years and i am willing to do whatever it takes to fix it...although i do live with my parents and i cannot control what foods they bring in the house