Mandy, It's very common on low carb. It's happened to me too. If the hair thinning is due to low carb/ weight loss shock, then according to all the documented stuff, it will grow back. Mine has started to grow in again, actually.
That's nothing to do with hormonal change or alopecia.
Biotin and B vitamins may also be good as extra things to take, but basically I think you have to wait.
You could look at Chris Kesser's Paleo blog on nutrition, resistant starch etc. He's good.