Well you are right in suspecting metabolic issues as the weight gain and the menstruation issues can certainly be linked to each other. The first thjing which comes to mind in this regard is that she could have athyroid problem which is causing the symptoms. Hypothyroidism can certainly cause changes in her periods and also cause weight gain, slowed reflexes, fatigue etc. this can be easily checked with the help of a simple thyroid function test. This would then be managed with a simple hormone replacement regimen.
Another cause of these symptoms can be associated with the adrenal glands. if her adrenal glands are producing more cortisol then usual that again would cause weight gain, weakned bones, fat around the belly among many other symptoms. this is known as cushings syndrome. This would be managed with the help of a several tests including a 24 hour urinary cortisol level.
Lastly these symptoms can also be the result of underlying problems with reproductive hormones like FSH and LH, PCOS or polycystic ovarian syndrome can sometimes also present in this manner and a simple ultrasound would be beneficial here.
Diabetes is one more condition which comes to mind here as well. the best solution here would be to see her doctor and discuss these possibilities with him, and if the initial tests point towards these then she should be referred to an endocrinologist.
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