Why did you gain weight in the first place? Overeating? Stress with people? Etc.?

stress. cortisol.

Cortisol?

Stress hormone aka cortisol + slowed metabolism (hypothyroidism?) + caloric surplus + salt(water retention) etc...

Oooi sayang, you have kinda posted the question and answered as well?!

Maybe you want to elaborate a little bit more on it?

Stress, depression...
Either eat junk food or spend saving on useless thing..
Which feel regret later...
Alrrady bad habit...

This.

Basically any extra calories from your body and it will be converted to fats or muscles, which contributes to lean/non-lean body mass(weight gain)

Felt like eating more carbs such as Rice can cause us to be fat

depression

instant noodles and chips. it is a love and hate thing

honestly i don't know..
maybe due to aging factor/ decreased metabolism..

It depends on various factor.

I have a guy friend that tend to contribute weight gain & loss with stress. Like he can put on 2 ~ 3kg in 1 month time whenever he have relationship issues... which contributes to his heightened sweet intake.

But at the same time, he can reduce weight 2 ~ 3kg in 3 months if he controls his sugar level and maintain a stress-free lifestyle.

I would say it depends on the individual and the environment.

Poor diet, lack of sleep, water consumption and exercises. These just to named a few.