Thirst is a hallmark of uncontrolled diabetes, but obviously may also be due to other causes.
First things first: is your thirst due to uncontrolled diabetes? I’m missing some key bits of information to help decide.
I’d like to know if your measured blood glucose (BG) levels, which you describe as 114 to 129, are representative of your around-the-clock levels. If indeed they are, and you don’t have any BG levels over about 180 mg/dl (10 mmol/L), it’s unlikely that your thirst is due to diabetes. The reason is that the thirst of uncontrolled diabetes is due to urinary loss of sugar and subsequent loss of fluids. In other words, if you pee a lot, you’ll get thirsty. So, measure your BG at different times of the day, especially several hours after large meals, to see if your BG numbers are intermittently – or perhaps mostly – higher than you expect.
Another way to assess if your thirst is due to high blood sugar is to measure urine sugar levels (something we don’t often recommend in the 21st century, although for many years it was the only way to assess diabetes at home). The urine is unlikely to have sugar in it unless the kidneys are presented with so much sugar that they can’t reabsorb all of it – which typically happens when the BG level is over 180. So if your urine is sugar-free, then your thirst is unlikely to be due to high BG.
If you have continuing thirst with near-normal BG levels, your physicians will have to look for alternative causes. There’s at least one rare endocrine condition that might be involved: lack of a different hormone, called vasopressin or antidiuretic hormone (ADH), which causes a condition called diabetes insipidus (DI). DI’s name’s is similar to that of the much more common diabetes mellitus, but DI is an entirely different disorder with different causes and different treatment from DM.
There are a lot of other possible causes of thirst, including drug side effects, psychologic causes, and dehydration. The sweating episodes are difficult for me to associate with the thirst, and should also be checked out. For instance, might your dose of replacement thyroid hormone for the hypothyroidism be too great, and causing the sweating?
I must respectfully disagree with your mum: withholding water may lead to dehydration and additional problems, and should only be done if instructed by a physician, perhaps as part of testing for what is wrong with you.
You should inform your physician that you are still thirsty and have sweating episodes, and together work out a plan to assess what the cause(s) might be in your case.
Parenthetically, I might also point out that in light of you having other autoimmune disorders (RA and Graves’), it’s more likely that your diabetes is also autoimmune. Typically, autoimmune diabetes shows up in kids and is easy to label as type 1 diabetes, but there are adults with autoimmune diabetes that doesn’t quite obey the usual rules – it’s called LADA
(latent autoimmune diabetes in adults). LADA is a different disorder from type 2 diabetes. If it turns out that you have LADA, you should plan to get started on insulin – you’ll need it sooner rather than later.