As per your query,you are having Hypothyroidism
.You should take Thyroxine
tablets orally after consultation with Endocrinologist
.He will decide the dose and you should have regular follow ups.
Regarding Gastric problems,please take Rabeprazole
Extended abdomen size,weight gain may also be due to Hypothyroidism.
If you come back few months after your treatment ,I can further guide you.
Wish you good health