A very academic explanation of this phrase is found  here . A military version of this phrase is "got your six." The saying originated with World War I fighter pilots referencing the rear of an airplane as the six o’clock position. If you picture yourself at the center of a clock face, the area directly in front of you is twelve o’clock. Six o’clock is what lies behind you. On a battlefield, your “six” is the most vulnerable. So, when someone tells you that they’ve “got your six,” it means they’re watching your back. By extension, that person expects you to have their back as well. “Got your six” is now a ubiquitous term in the military that also highlights the way military members look out for each other. ( source )

No clear origin is found for this term but it generally means that you have found yourself in a messy situation where no solution/resolution is apparent.  But sometimes the phrase is flipped to motivate.