Why am I struggling so much?

When I was 18 I had gotten birth control, I got the implant, you know the one that goes in the arm. Ever since I started gaining weight. I was skinny my whole life. I finally got off of it at 21. I am currently 25, standing at 186 lbs at 5'4". I am supposed to be in the 120-140 range. I am currently 46 pounds over weight. I am so tired of being overweight and have been doing everything I can to get it to go back down. I just seem to envy someone I know who lost weight with seemingly no problem. I continually seem to struggle. The only thing I can really blame is my current situation at home. Me and my fiance are living with my parents, I take care of the house and my grandmother. I have little control of what is bought food wise. I feel so stuck and depressed about it all. I want to be healthy again, I want to feel confident again. I doubt anyone is going to even read this, I honestly just needed to type this out.