How to pump while LO is cluster feeding?

Jennifer
My 3 week old cluster feeds from about 3-8pm everyday.  By the end of that, I end up giving her an expressed bottle for the last feeding before bed. I can't find any time except for in the morning or overnight because she is constantly on me. Any advice on how to do this to build up a stash? I'm not even sure she's getting enough during all of the clustering and seriously my boobs need a break !