100% sticking to a calorie deficit but not losing weight??

I am a 31 year old F. I am around 164cm.

I have been in a calorie deficit for about 6 weeks now. I initially lost around 2.5kg within the first few weeks but have now been stuck at 83/84kg for the last month.

I have been counting every single calorie I eat. I eat between 1500-1600 calories every single day. I weigh sauces and don’t use oil. I also haven’t been eating fast food.

I have been pretty sedentary however started running a few times a week and have now began lifting weights. I also have started walking for at least 30 mins per day.

My doctor recently let me know I may have a lazy thyroid and I am currently waiting on further blood tests. I also may have PCOS but my hormones seem ok - I have high insulin.

I am on the contraceptive pill and 5mg endep for pain management.

I am going crazy. I sleep 8 hours per night and drink around 3L of water per day.

I know most people who aren’t losing weight aren’t in a deficit but I know I am! I also have a Garmin which says I burn around 200-500 cal per day. My TDEE is 1800cal.