My baby is 7n half months old she is not yet sitting by herself.. Even she is not putting her weight. Her birth wt was 2.3 kg now she is 6.3 kg is it normal or shld I do something else

A. babies sit at 6-8 months to encourage the baby use Babyhug booster chair or Babyhug high chair babies double the birth weight at completing 4-6 months and three times the birth weight at completing one year growth is good