Unhealthy relationship with food?

Hi, I am a bit nervous to write this but just looking for some advice really and if anyone else is in the same boat. Long story short, since around the age of 15 I was obsessed with my weight and calorie counting. I pushed myself to be at the very lowest scale on the bmi chart for the 'normal range'. I would frequently skip meals or eat something very little, and would always look for low calorie snacks otherwise I wouldn't eat them. I also purchased meal replacement shakes at one point. Fast forwards 7 years, I am now out of an extremely toxic and mentally abusive relationship (which started about same time I became obsessed with my weight and calories), and now in a happy relationship with a supportive partner. During the first lockdown in 2020 I put on quite a lot of weight which changed how my body looked a lot. I did begin to lose some of it again in autumn, but by the second lockdown from christmas to april 2021 I have put it on again and more. I am really struggling with my body image right now and I feel sick at the thought of my body. I want to make a change but I have no motivation and I am also worried I may slip into old bad habits with obsessing over weight and calorie counting again. I guess I'm just feeling horrible in myself as I really do not like my body and it is really starting to get me down and affect my mood/mental health. Thank you.