3 weeks old, let her sleep?

So I've been awake for the last two hours because my baby has been grunting and groaning in her sleep dealing with some gas. Prior to her going down around 10:30pm last night she was awake for almost two hours with bad gas, screaming, cluster feeding every half hour and she was SO tired but wouldn't sleep. Now she's been asleep for about 5.5 hours since the last time she ate. My boobs hurt! Should I let her continue sleeping (never wake a sleeping baby) or get her up to eat since it's been so long?? I've been hesitant to fall back asleep since she has never gone more than 4 hours between feeding. Thoughts??