HOW DO YOU KNOW IF YOURE OUT OF MILK??

K • Baby E 3.1.17 💙 Baby B 2.25.20 💙 Baby due Nov '22
My baby is 7 weeks old. He's been nursing virtually nonstop for the last 4 hours, & whenever he does briefly stop, he fusses & cries. At this point my breasts are feeling pretty slack. How do I know if he's getting milk?? Could I just suddenly have run out somehow?? I've been EBF since he was born. Please help!! 😕