My baby completed 7 months today. Her birth weight was 2.4. today her weight is 5.8. She is still not able to hold her neck properly. when we give her tummy time she doesn't lifts her neck. also she doesn't lifts her legs. she moves legs but can't lift. her social smiles are normal. she can recognise faces. if we show some toy to her she grabs it and puts in her mouth but can't lift her hands from shoulder. pls guide...