DD will be 5 months on the 12th. I don't mind rocking her/helping her fall asleep to take a nap as it usually only takes 10-20 minutes, which is reasonable to me. BUT lately she has only been sleeping 10-20 minutes after putting her down & it's making me crazy! Sometimes she'll wake up smiling (she's a generally happy girl) but sometimes it's abundantly clear in her attitude that she needed a better nap. I've heard that nap training can lead to longer sleeps, is this true?