My 7 week old (4 weeks adjusted) can hold her head up and turn when resting over our shoulders. She can also somewhat hold her head up (a bit wobbly) when we sit her on our knee and she is upright. But when we lie her on her tummy she either isn't interested or doesn't have the control, not sure which. I've seen her lift her head and chest a few times while on her tummy, but so inconsistently. Should I be concerned? What could your lo's do at this age?