Hi.
Thanks for your query.
Noted the history about a 22 year old lady and understood the concerns.
Grave's
Thyrotoxicosis itself can cause many a gastrointestinal disturbances like loose stools, menstrual changes and so on.
Carbimazole is the drug of choice and if it has started causing so many problems then you can discontinue to see if stopping Carbimazole helps to abate the symptoms of gas and
bloating.
If this is so then you may have to stop the medications and go for the thyroid reduction surgery , although it needs a lot of preparation before surgery.
Also needed is the tests of blood particularly for CBC to see whether Carbimazole has caused any changes and possible
bone marrow suppression or any other problems.
If the stool shows any infection, a course of an antibiotic and
metronidazole can help you to have good control.
Also identify the foods and beverages that are causing such problems and stop these altogether.
It is imperative to rule out other causes of your symptoms so that a proper cause be found and treated accordingly.