Hi I am new to this site, but I thought I'd respond to your post, because I have been going through the same thing with my DD. It started at about 3 months (she is now 4 3/4 months). She learned to roll from her tummy to her back at 12 weeks and then from her back to her tummy at 16 weeks, since those milestones she's been taking shorter naps. I used to be able to shh/pat her back to sleep at the 45min mark, but not anymore! She just arches her back and her little head looking all around wide awake. I feel your frustration! My DH has to reasure me almost on a daily basis that I'm doing a great job and am a good mommy, but it's hard to watch your child get crabby after being awake for only 45 mins because she hasn't napped well!
Ughhhh all I can say (since I'm rambling on now) is that after trying everything myself ( I am now trying to extend her awake time slowly every few days), I think some babies just have to ride it out and eventually they will begin to take longer naps (I hope). I've combed the sites looking for answers (since my Ped doesn't have any advice), and it seems that is one thing that comes up, that they work it out on their own and that all we can do as moms is just be as consistent & patient as possible. My DD has been a self soother and able to fall asleep on her own from about 3-4 weeks, so I know that is not the problem and she has been sleeping through the night from 6 weeks and now sleeps from 7PM-6AM or so. I guess that's why this is so frustrating, she is able to sleep great at night, but why the easy awakenings during the day?
? Here's my last tid bit, and some people may say I'm crazy but this is what we've done to try to solve the nap problem:
*Installed black out shades
*White Noise machine (from Brookstone, works great for puppies too)
*Installed an air conditoning unit (we live in Hawaii and it gets really hot in her room)
*Turned off Phone ringers during nap time
*Stayed home for days on end to try and work out the problem
*Hovered over her crib at 35 mins to try and "catch" the stirring w/ a shh/pat & stayed there for up to 45 mins w/ shh/pat off and on...it's exhausting, sometimes it works, but not often
*Consistant nap time routine
So now I try the extended awake time, slowly of course, because I feel that at almost 5 months she should be able to stay up longer than 1.5 hours without having a melt down. I don't think I have any advice here, but just some support for a fellow mom who is also at her wits end. Hang in there!!