Yup, have been through all this...20 minute naps...won't settle....grizzles all day through tiredness..blah blah blah. Very stressful, and I too have spent whole days trying to settle dd. Eventually in desperation went to doctors where she screamed the place down.
What worked for me is "The Baby Whisperer" Not the routines particularly, but the methods of getting them to sleep. Incredibly helpful, I think I would have gone mad without it, and Hv of course was NO help.
Dd is now 5 months old, and sleeps well in day. She still wakes up early, but grizzles herself back to sleep after about 10 mins.
That book is GOD! However apparently it is also a developmental thing, and they improve as they get older.
Have to say, there are always loads of threads about this, perhaps babies who don't nap well during day should be part of ante natal classes. As for that crap "sleep when your baby sleeps", Pah!Can you get to sleep and wake up refreshed after 20 mins?It's ok if your baby naps for 2 solid hours.
Hope this helps and it should improve eventually..