My boy Hunter has a similar problem except he would have a series of cat-naps lasting around 30-40 mins a time which is not long enough. Finally, out community health nurse gave us some tips and gave us a home visit to guide us one afternoon. The results were almost instant (very positive!) so I suggest utilising the skills and resources of your local community centre. Failing that, this is what helped us:
1. If you have a monitor, don't use it. Get rid of it or only use it when absolutely necessary (if you'll be in the garden etc.)
2. Observe tired signs and begin a routine for preparing for bed before he gets too/over tired. We stopped wrapping/swaddling him at 8 weeks but if you still do so, start with that and give him a few minutes cuddle/quiet but don't let him fall asleep in your arms. It's important to not stimulate him when preparing for bed which means no or very limited eye contact , no talking except for low-level 'ssh' and no smiling from when you see him getting tired.
(if you're not sure what his tired signs are, put him on his mat and observe from a distance as he won't want you to see him getting tired. Watch for frowning, yawning, eye-rubbing, jerky movements, fist/thumb sucking, head moving side to side etc.)
3. Put him in the cot awake with no eye contact, comfort him and leave the room if quiet. If he's crying, you have to wait until the crying gets to the medium/high level then time 20 minutes before you go to him. This is to allow him so learn how to settle himself. You'll notice different cries.
Follow Karitane or Huggies guidelines on how to settle (on side, patting nappy etc.)
4. I found a radio on low background noise or a fan helped. Even a tv in the background gives them a consistant sound to listen to.
He needs at least an hours sleep each time. If he wakes befoer then, don't react immediatly but allow his cry to intensify before attending to him as he may resettle himself.try to resettle for however long you can manage (i gave him 20 minutes)but if he doesn't, put him in the pram, in the car or on your chest and continue quiet time until and hour is up.
we saw results within a few days and now Hunter is sleeping through the night (from 6.30pm to 6.30am!) and having 2-3 really good sleeps...I even have to wake him sometimes and he is so much more of a joy. Not to mention I'm more relaxed!!!
Good luck. Sorry if it's a lot of info but it should work if you stick with it!
northern nsw, Hunter born 22/2/06