6 week old feeding for 40/60 mins every hour!

My LO is 6 weeks 2 days old and breast feeds for an average of 40 mins at a time ( using nipple shields, which we are trying to get rid off). She is a slow feeder and sometimes she falls asleep and then remembers and goes back at it. After feeding she is content and relax but most of the time she only sleeps for 25 mins and starts crying for more boob. Basically she feeds for 40 mins every 1 hr 30 mins! Is this normal behavior or she simply is not getting satisfied enough? She also poops and pees frequently (4/6 poopy diapers a day).