Milk supply basically gone

Edit: I do have hypothyroidism I don’t know if that makes a difference.

The last week I’ve noticed my baby doesn’t want to nurse very much but will drink formula. As a result my supply is basically gone. Or it could be she’s not getting enough from me and that’s why she prefers formula? I’m ok with doing formula I guess as long as she eats but is it normal for milk to drop like this at 6 mo? If so will it dry up on its own. Right now she really only nurses for 13 min when she first wakes up and then maybe 2 minutes sessions randomly throughout the day. I’m a FTM so I don’t know what to expect or do.