Hashimoto's Disease - Terribly Low Vitamin D And Thyroid Level 13

Over the last year and a half, they have been testing my thyroid as it keeps showing up as underactive (no they have not done anything about it, for some reason they just keep getting more bloods done?). Until 2 years ago, all of my bloods came back perfect, with a high iron count of 148, but the other levels pretty much smack in the middle of normal ranges. This time, My iron came back as 53 - the doc said for me this is quite bad because mine are usually so high. My Thyroid level was 13, and he told me that my Vitamin D was terribly low. Although he did not give me the exact level of Vit D, I can only assume it was rather terrible as that is the only supplement he told me that I need to get onto immediately.

So, I know these levels are not great, but as it was a rushed appointment, he told me those levels, told me that I have Hashimoto's Disease and wrote up another batch of blood tests. So now I am lost.

Can anyone tell me what on earth this all means?

I AM going back to him, but couldn't get an appointment until mid/end next week (which is great because my bloods should be back by then anyway).

This will be the 4th set of bloods I have done in the last 18-20 months, all of which showed an underactive thyroid. I'm just not sure why they are still testing?

Is this normal? And what do those iron and thyroid levels mean? I'm assuming it isn't anything drastic or he would have done more about it?