How old is your Baby?
If Baby's younger than 4-5 months, his back may not be in a curve because:
- He just woke up, he's stretching
- He's fussing
- He needs to pee
- Straightening his back, and trying to find support can be a way of expressing his anger or discomfort
If Baby'older than 4-5 months :
He has acquired better head control and stays awake for longer periods of time. When he's worn during waking moments, he may straighten his spine even if he's in a correct position. That is quite normal, the spine will go back to a rounded shape when he's sleeping - this guarantees good back support.
7 months-old Baby, awake and looking around - his back is straight :
7 months-old Baby, just waking up and not active yet. He's nursing, his spine is in a curve :