What terrible advice from a so called doctor!!

DD1 was a terrible day sleeper until about 6 months (but oddly an amazing night sleeper AND in her bed). It bothered me no end and I was constantly upset about it until I realised that going with the flow was far more relaxing for both of us so I wore her in a sling, for all her day naps. I went out quite a lot too (visiting friends or family, to the shops, etc) as I felt much better being out and about and she slept fine, as long as she was in the sling. She also loved her dummy but only for sleeping generally.

So my advice is just wear her My DD1 randomly started sleeping in her cot for day sleeps at 6ish months. I recall I was expecting visitors and thought I'd try her in her cot for her nap and she slept for over three hours straight. I was gob smacked and we never looked back after that.

DD2 is a completely different kettle of fish. She's slept well since day dot and still (easily) has brilliant day sleeps in her cot. She'd actually prefer to be in her own bed than 'on the go' as she happily sleeps for 2-3 hours at a time. I feed her to sleep (or rock her, cuddled in quite tightly, if she's not interested in the breast). She also has a dummy for sleeping and wears a sleeping bag with Sleepy Wings (google them). She likes to have her hands covered and a bit restricted, even still at 7.5 months so that always helps her sleep. In the warmer months and when she was little, I user the Love to Dream swaddle bags. They could possibly help your DD?

Reading sleep cues is really important as well but there are definitely plenty of babies who just like to be held when they sleep and a sling or carrier makes that a lot easier.