The symptoms you describe could fit with an underactive thyroid gland but the bad taste in the mouth, cough and fullness in the throat could also fit with gastrointestinal acid reflux. The thyroid gland is located in the lower aspect of the neck and can become enlarged when it is not functioning properly - the medical term for this is a thyroid 'goitre'. A hoarse voice, weight gain, tiredness, skin changes, sluggish bowels, depression and blood pressure problems are also seen in hypothyroidism although you do not need to have all of these to raise suspicion. Stomach problems are less likely to be directly related to an underactive thyroid gland and although a gastroscopy will help shed light on gastric acid reflux it would not be able to give information about the thyroid gland. A thyroid blood test is a key investigation to detect thyroid dysfunction. If you have noticed enlargement of the thyroid or have detected any unusual lumps in this area it is important that you have further medical investigation of your thyroid gland.