Hunger cues

Hi mummies. My LO is 13weeks already. She is at the stage where she suckles on her fists to soothe herself. Her drinking pattern has also changed, sometimes can be 2 1/2hrs sometimes can be 4hrs. It’s difficult to tell if she’s really hungry, the way she sucks her fist is quite fierce. She’s my first baby and I’m confused and dunno her hunger cues anymore… 😥