Home is my weight loss nightmare!?

When I was away at college this past year I lost around 50 pounds and was much healthier. I exercised regularly and I ate very healthily! I've been home for summer around 2 months now and I've gained 27 pounds! 27 pounds in two months! I feel like a crazy person when I look at the scale but I mean it's the scale it doesn't lie. I don't know what to do! I'm the only overweight person in my family and my mother is really insensitive to my situation. She is in complete denial that her cooking is terrible for me. I've asked her to be conscious but she really can't be because I have siblings that have no interest in health. It also doesn't help that we constantly have junk food hanging around! I also live in a city and I refuse to purchase a gym membership for the whole year when I only spend 3 months here. I don't know what to do. I feel so shitty and disgusting. I feel like a fat piece of crap.