i don't get it

caleb used to be hard to put to sleep and then we worked and worked and it got better. and then it got easy... maybe too easy. and now it's gotten really hard again. he just cries and cries and won't calm down. i don't understand why he goes through such phases... and i want this one to be OVER! i need his nap times, and when they don't happen when they should it only makes us both grumpy.