My Daughter Is 6 Weeks Old And She's Approximately 7

My daughter is 6 weeks old and she's approximately 7 pound's. She was born 3 weeks premature but she's been healthy. In the past 24 hour she hasn't wanted to eat much at all and she's been constipated. She doesn't have a fever but I'm concerned with her not wanting to eat. Could she be getting sick? Should I take her into the hospital?