Sad baby :(

Liam is always so happy, and he has never been one to cry, mostly just grunt ha but tonight it's like something snapped in him and he has been bawling till he is red in the face and nothing can calm him :( he keeps acting like he wants to nurse but he just puts his mouth over the nipple and screams!! He ate a lot before so I don't think he's actually hungry but idk what's wrong, he just keeps crying!! I checked his temperature and he's fine, idk why he's so unhappy??? He's one month old tomorrow...