Getting discouraged...

JS
My baby is going to be two weeks old tomorrow, sometimes she feeds for 20-30 minutes and sometimes she want to feed for over an hour. She was a small baby born at 37 weeks so they told me to wake her up and feed her every 2-3 hours and could go 4 once a night. They said once she got back up to/surpassed her birth weight that j could start feeding her on demand. Sometimes I still wake her because she'll go well over 4 hours if I let her but the feeding for over an hour seems crazy. At first I had a large supply but now it seems like there's nothing there. I can squeeze some out but it definitely isn't as much as it used to be. Has anyone experienced anything similar? Is something wrong? I am just about ready to give up!