How to Second letdown?

Jillian

Hi there! FTM here and I'm exclusive pumping due to nipple issues. I know this might be early but tomorrow marks one week PP. I have a spectra pump and am pumping every 2.5-3 hrs religiously. My breast empty quick, like in 5 minutes then I pump for 5 more with nothing else out. I've tried pumping for 20 minutes and hitting the letdown button again with no luck. Any tips? I get crazy about how much my newborn is eating 70ml a feed at 5 days and how much I have stocked ! Help!