Hi!
I did this, too, letting my babies (now on my 3rd) cry it out so they would learn to go to sleep on their own. It seems like torture, especially for the mom listening, but like you said it only lasted a couple of days. As for the 45 minute naps, the book i read about teaching your baby to sleep says a true nap is one and a half hours, with 45 minutes as one sleep cycle and the next 45 minutes are a different part of the sleep cycle. I can't remember the terminology. (REM, etc) So your baby is probably waking up cranky and now getting cranky due to lack of sleep. I let my babies fuss a little at this time, too. It again will probably take a couple of days--we especially did this with night waking. Either I would let them cry and see if they would go back to sleep or I would go in and pat them on the back and say "Go to sleep" which usually made them cry more because then they were mad. At night, I would make my husband go in and pat their backs so they knew Mom wasn't coming in to get them. Initially, I went in so they knew I heard them crying but that I wasn't getting them. Then after a couple of days, I let them cry it out without seeing me. It did work and I did have happier babies--now with my 3rd, the babysitter can lay her down and she goes right to sleep and takes good naps.
Hope that helps. I hated hearing them cry, though, but I figured they wouldn't remember it and crying never hurt a baby so I would watch the clock.
Happy Mother's Day
M.