You make me giggle at your excitement for running.......... I've always wanted to be a runner - but never had the stamina for it. And at my age - I don't think I'll be giving it a try.
I think the advice on the whole30 is probably right on. Our bodies do get used to things and they don't respond the same after a bit. I'm wondering if throwing in some new foods might help shake things up? Try a meat that you've never had or change up your veggies? I don't know - maybe you already have a wide variety and it wouldn't make any difference. It sounds like you're getting enough carbs though.
It'll happen -- let your body adjust to this new weight and then I'm sure it will start to drop again.