Baby sleeps on side or stomach


So my baby is 2.5 weeks old and used to sleep anywhere and on anything. Now, if she’s in her boppy or crib she wants to be on her side or stomach and will not sleep on her back. She will cry and fuss until she spits up if we put her on her back. She won’t sleep on her momaroo swing and I am a bit nervous of letter her sleep on her stomach. Anyone else have this and what did you do to help??