Hello Missed period form last 6 months weight gain , abdominal pain swelling in a female in child bearing age may be due to . Poly Cystic ovarian Disease ( pcod ), as this is most common cause . Diagnosis can be confirmed by ultrasound of abdomen and both ovaries . Also get in hormonal test. 2 Second reason may be tumor in adrenal gland so get in a M R I for confirmation . 3 Obesity may be the next reason due to excessive eating . As obesity causes headache , swelling . Sometimes fluid retention may be the cause of such swelling and pain abdomen. In my opinion first of all consult a gynecologist and get his opinion.