Thanks for writing to health care magic.
Normally babies sit with out support at around 6 months of age and by around 11 months of age stand with some support.
A variation of few months may occur in some babies.
What is the head circumference of your baby now. This will give a clue if the baby's head is growing normally or not.
A thyroid profile can always be done to rule out hypothyroidism
as this is a correctable cause of developmental delay.
further investigations may be required after clinical examination.
Hope this helps.