I agree with Samijoe
My DS is on a 4 hr easy, has a two hour nap in the morning and two seperate hour long naps in the afternoon and sleeps solidly from 9pm - 6.30am
I am aware that this is not a complete 12 hour day nor as it says naps should be in the book but he is very happy and we are getting there slowly,
He too had difficulty staying awake when we moved to 4hr easy, he can still only managed over an hour in the morning
your baby is almost 4 months old so as he gets older he will be able to stay awake longer and the naps may sort themselves!!!
xx