You have not provided us enough information to diagnose your problem. Could be leaks (such as that caused by strong reference cycles, e.g. sloppy use of repeating timers). Could be abandoned memory (such as caused by some circular logic in your navigation). No way to diagnose on the basis of what you've shared thus far.
I'd suggest you watch WWDC 2013 video, Fixing Memory Leaks (for registered developers). This builds upon the WWDC 2012 video iOS App Performance: Memory, which you might want to watch first. These walk you through the categories of problems and introduce you to some techniques for using Instruments to diagnose the problem.