@gemlou84 welcome to the T2 club
Sorry to hear your diagnosis, I can understand how you must feel. On the positive side though, it is early days though, and you have caught what is happening early and you are young. Well done for testing your BG (blood glucose) levels and spotting the rise.
The underactive thyroid could well be key to both your BG levels having risen over time and to your high cholesterol. The positive news is that it can be addressed. The majority of the cholesterol in our bodies is produced by the body itself rather than consumed. So do not blame yourself or your diet for this. Right now a low carb diet is going to be good for you in all aspects, also just because you go low carb it doesn't mean you need to go a lot higher in fats. Increase your protein intake with whole foods like eggs, meat, fish, you'll get enough essential and healthy fats. High carb diets lead to more cholesterol production by the liver. Too much fat will still potentially lead to insulin resistance, as any excess calories gets stored over time as fat. If you consume lots of protein you will feel full on fewer calories and your desire to intake higher energy fats and carbs will be diminished. Your body composition will also change, more muscle, less fat, giving you more metabolic flexibility. But still, do not consume more calories than you need to maintain a healthy weight. Keep tracking you BG levels.
Hypothyroidism can lead to increasing BG levels over time, initially it causes BG levels to drop but over time it can lead to insulin resistance and a rise in BG levels and eventually T2 diabetes. BMI can be misleading on an individual level in terms of understanding how much body fat you have and especially where it is stored. So set that BMI aside for now, I would humbly suggest. Also Hypothyroidism leads very often to higher cholesterol levels.
Proper treatment of your thyroid condition and a good diet will see you most likely return to good BG levels and have a good, healthy life ahead of you. Do not get too disheartened or too anxious.
You will need to do some research and have informed conversations with your GP so that you get the correct treatment. Sadly they always just go to statins when they see high cholesterol now. They did with me, and in my case it was absolutely the right thing, my thyroid tests were fine and I had very high LDL Cholesterol, Total cholesterol and Triglycerides, it is familial. I exercise a lot and my diet is good, that doesn't change my lipid profile for the better (apart from keeping my HDL in a good place). It is genetically inherited, statins make sense for me given the levels and ratios etc. It is complex stuff .. people are too quick to discard them as an option when for some it is actually the right drug. But for many it is not, again in my humble opinion. Inn your position I would get the GP to address my hypothyroidism first and see if that, along with good diet and exercise changes the lipid profile. See below for a couple of videos that will get you started on the road to arming yourself with some info to take to your next GP consultation. If fixing your hypothyroidism still leaves you with high LDL cholesterol AND a blood lipid profile that looks risky then sure, statins may be the right option.
The thyroid to T2 diabetes connection:
The thyroid to high cholesterol connection:
Good luck, one step at a time. Do not panic, nothing bad is going to happen anytime soon. Plenty of time to get things sorted. And seriously well done for tracking your BG levels and catching this early!