When I turn on our shower faucet, the water coming out isn't hot, just cold water at a flow that's not the usual flow.

When I turn on the hot and cold water from any other place in the house, I get water no problem.

We hadn't used this problem shower for 2 weeks before finding out the problem and are afraid that perhaps the pipe is frozen while we were out, but don't understand how that would be possible given that we've had the house heated to 55 minimum and the shower is the most interior of all showers in the house (meaning if this one froze, it's likely the others should have but for some reason didn't).

Any thoughts on what may be going on and what we can/should do? We're right now just waiting for a warm day to try again, but that seems to be less than ideal. Thanks!