My bub is 3 months old and I've been having a hard time trying to resettle him in the past two weeks. Before, he used to be able to nap for up to 2 hours but now he always wakes up after 40 minutes and I can never resettle him again. I've tried the following with no success:
- going in before he's fully awake and patting, rocking him
- put the dummy in and played a white noise CD
- even picked him up and cuddled him
- left him to cry
- taking him for a walk in the pram
- co-sleeping

Is this a phase they go through or is there something else I should be doing? Putting him in a sling is bad for my back so that's not an option.

Help!