No advice I'm afraid but my 13 week old is the same. She will sleep longer if she's held or in the sling (sometimes!) but really I think she's a cat napper! She sleeps 12-14 hours overnight (with dream feeds) so I'm just rolling with it.
Thanks for your reply! If I'm out and about our little one will sometimes sleep longer. She's been in hospital for a month so I think she's still adapting to feeling better and life at home. She's still not used to the car seat or the pram even. Like you, she is fairly good at night so I can't really complain. Just wondered if her naps should be lounge or ideas on how we can try and help extend them. X