Hi,
I would recommend you to read the book by Dr. Marc Weissbluth "Healthy Sleep Habits, Happy Child". I have a 6.5 months old girl. She has been sleeping through the night at 1.5 months, but then at 4 months I started noticing that someting was wrong with her sleep schedule. She started waking up more often (not to be confused with growth spurt) and at nap times it was really really hard for her to fall asleep. Well, I read this book and came to conclusion that she was overtired and sleep deprived. Her naps were very short because she was destirbed by her older sister who is 26 months old now. I put her on schedule for "4-8 months olds" form the book. Here is a little example:
7am WAKE UP
9am 1ST NAP (1-2 HOURS)
1PM 2ND NAP (1-2 HOURS)
4PM 3RD NAP (1-1.5 HOURS)
7PM BEDTIME
The book gives more details about the schedule, but it helped me a lot. Now I just have to nurse her, turn on soft music, put a soft blanket near her face and she falls asleep by herself (Without rocking her to sleep, crying or anything else, with some exceptions).
Well, hopefully my advise will help somehow.
A.,
a mother of two yr old and 6.5motns old girls.