My DD is nearly 8 months old. She sleeps well at night (wakes up once but goes back to sleep after a feed) and has a good morning nap of about 1 1/2 to 2 hours. Until about 2 weeks ago she was napping quite happily after lunch for 1 to 11/2 hours, but suddenly that has stopped. She now cries and won't sleep. I've ended up having to take her for a walk and she eventually sleeps for half an hour but quite late in the afternoon. Any ideas?