Hello
@Chloelox - I have an underactive thyroid and before diagnosis I was fighting insulin resistance, it took a around a month or 2 once I started on thyroxine to get my levels more manageable but only when my dose for my thyroid was working effectively, so be prepared that even once you start taking medication it can take a while for things to settle down again but it will improve, it's all a balancing act though as all hormones have a part to play in the role of insulin requirements.