9 month old not sitting alone

[letsstickmyhandinthere]

My ds is 9 1/2 months old and refuses to sit up unassisted.
He army crawls and rolls happily across the floor but has literally no interest in sitting up. I've tried wedging him upright and tried bumbo seats ect but nothing seems to work. We have his 8-12 month review in 2 weeks and I'm worried about it. He's my 3rd child and both of the other two has mastered sitting up by 8 months (both are hypermobile)
He's not interested in pulling up either.
Is there anything else I can do or is he just lazy ?

Bump

I don't think babies can be lazy really, they do what they are capable of doing. One of mine was a very wobbly sitter until about 12 months, although could technically do it from about 8. I think you'll have to ask your GP, but it definitely doesn't mean there's automatically a problem. All the rolling will be strengthening his core to sit.