Let us review some common factors associated with weight gain.
Age - At your age, many of them tend to gain weight. It could be reversible or irreversible.
Increase in
caloric intake and
Alcohol- Knowingly or unknowingly, one tends to eat more. Alcohol can also cause weight gain.
Decrease in
physical activity level- Which doesn't seem to be an issue in your situation.
Medications:-
Steroids can cause variable weight gain
Antidiabetic medications are associated with weight gain.
Antidepressants- Many of the
antidepressants medications are associated with weight gain.
Oral contraceptives are associated with wieght gain.
Depression and stress themselves are associated with increase food intake, knowingly or unknowingly.
Just to list some
Endocrinologic disorders:-Cushing syndrome
HypothyroidismPolycystic ovary syndrome
Hypogonadism
So to sum it up, weight gain could be due to a single or multiple factors. Last but not the least, having positive attitude towards life always helps. I tried to give you a rough idea but you need to see your doctor and the dietician regarding this. I am sure you will see positive results with time and proper counselling.
Wish you best luck.