Bathroom water not running! ?

it is an extremely cold winter day in chicago and the cold water in my upstairs bathroom isnt running. so immediately i think the pipes are frozen. the water in the kitchen and downstairs bathroom work fine and come out with normal pressure. even the cold water of the bathtub in the bathroom im talking about comes out with great pressure. its just the sink cold and toilet that arent coming out at all, no trickle nothing and the toilet and sink are not located near an exterior wall. i can really see where the pipes lead to because there is drywall covering everywhere the pipe is going. what should i do? help??