any tips on getting babies in a schedule

To sleep longer at night?! I love my daughter to no end and I would do anything for her but I am soooooo desperate for sleep!!! She's almost 3 months and she is waking up every 2 sometimes if I'm lucky 3 hours to eat and her pediatrician said she's at the point where now we can train her to eat every 4-5 hours at night and to just give her a pacifier at night in between if she wakes up... I tried it for two nights and I just felt so awful I ended up feeding her. I didn't want her to be hungry :(