Thanks for query,
First rule out diabetes
and thyroid problems.
Go for blood sugar, fasting and post lunch,
Thyroid function tests
As you are gaining weight is unusual so rule out above conditions.
Do regular exercise,like running,swimming,jogging.
take less fat and carbohydrate
,More green veges,salads, fruits.
Avoi ried,spicy and junk food.
ok and bye.