Is this your GI who blew a gasket? If so, whatever; ignore him.
Since he's pushing a lifetime of pred., what's three weeks to wait for an endocrinologist? Hormone balances are misunderstood by nearly everyone, even (or especially) doctors, and until you have an better opinion, your doc today amounts to so much water under the bridge.
A word of forewarning, though, you're going to want to make sure even the endocrinologist knows what he/ she is doing. Many of them specialize in thyroid or fertility issues and have limited range of professional knowledge and practice outside those interests.