Some kids just need reassurance.

DD1 has always self settled pretty much from day 1. I never sat with her, sang, read books. We never had a routine until she was 6-8 months old (thanks to a great chicky Tara who helped me soooooo much..love ya babe). Now at 15 months she is a gem. Bed no problems day or night.

DD2 was in our room until 8 weeks old...and from then on she settled herself.

I think kids get used to 'mummy does this and this then i do this and that' after a while. Maybe try a comfort toy, blanket or something your baby associates sleep with?

DD2 knows at night when she gets wrapped its big sleep time....sleeps through 10-12 hours a night no wake up for feeds or anything.

DD1 knows when she is put in bed with a dummy and her pink dolly (Isabella) is sleep time.