Weird question and need HELP😩

So over the last few years I’ve gained about 40 lbs. I was on birth control that made me gain weight also lack of moving and some serious carb loading. I’m talking fast food 3 times a day and laying on my ass all day long, (depression) I’m surprised I only gained 40 lbs to be completely honest. In the past I have started workouts and eating healthy and I lose weight really fast. I always have. I gain it fast but I lose it fast as well. I downloaded an app that says my goal to lose 40 lbs will take a pretty long time. I’m confused because they say the slower you lose it you get lasting results. The problem is I don’t do it unhealthy and I want it to be slower so I have lasting results but that just isn’t the case with my body. For example I ate very healthy and worked out for 2 months and lost 30 lbs. Is this normal?