my life has changed completely

I was diagnosed with Hashimoto’s last year in the summer. I take 50 mg of Euthyrox. The doctor didn’t tell me to follow a specific diet, but even though I wasn’t eating more than 1000-1200 kcal, I still couldn’t lose weight, so I gave up dairy, gluten, and sugar. I find it very hard to stick to a diet, especially when it comes to sweets. I think it’s an addiction I’m fighting. What bothers me the most is that I’ve gained 12 kg in four and a half months, and I feel very bad both physically and mentally. I’ve started to come to terms with it and to work on losing weight. Sometimes, I feel like my face is swollen, and I also have a double chin. In any case, what advice do you have for getting rid of the double chin and losing weight? How do you motivate yourself to stick to a diet? Is there any way I can get my face back to its original shape so it’s no longer swollen?