with (one's) back to the wall
In a bad or high-pressure situation in which one's choice or ability to act is limited. She finds herself with her back to the wall now that creditors are coming after her for more money than she makes. Sometimes, the best solutions arise when we are with our backs to the wall, when we don't have the luxury of examining every option under the sun.
with your back to (or up against) the wall
in a desperate situation.