Hi -
I read through the other responses. Pretty consistent with what I have found when I have posted for sleep help. You will have to choose if you are comfortable with CIO, if want to do maybe a bit of it but not hard core CIO, or more of an attachment parenting thing where you are soothing.
My little one is 5 months, but almost 4 months developmentally since he was premature by almost 7 weeks. I am in the middle of the sleep crazy thing too, and just requested books from the library to help me through it. I have the Weissbluth book, love the info on sleep research and how to understand where babies are at with sleep, but don't think I will do his extinction method, which is hard core no matter what cry it out. So I am getting the books, Sleeping Through the Night by Jodi Mindell, Happiest Baby on the Block by Harvey Karp, The No Cry Sleep Solution by Sears and Pantley, The Secrets of the Baby Whisperer. I have heard over and over from non CIO parents these are books they found helpful. My sister thought the Mindell book was the most helpful one she read since she is not a cry it out person, but she has not looked at The No Cry Sleep Solution book or the Baby Whisperer. My sister just got their 5 month old sleeping from 9:30 to 5:30 or 6am using those techniques. It took them a couple weeks, but they did not do cry it out and they did it while weaning her from her pacifier. She just did this a week or two ago. She has 3 other kids, has not done CIO with any of them and they are good sleepers.
So do some soul-searching (or do a trial of CIO and see if you can handle it - that is what I did and it reaffirmed I could not even in my most desperate for sleep moments about a week ago). I am thinking our little babes go through something around 3 to 4 months where they really start fighting sleep. As my little one became more social with us, he stopped wanting to sleep as well because he didn't want to miss anything. That is when our sleep fell apart. We basically lost naps for a while and he woke more in the night for a while. He is getting back to being "better" at night (most of the time a good 4 to 6 hour first stretch, then usually a 3 hour stretch), but naps are still really short and a struggle. He is breastfeed baby, and rather than giving him formula before bed (research does not support formula or cereal makes them sleep longer, although formula moms swear by it) I pump and we give him a bottle so I know he has had a good amount. We actually do this for his first wake up too, so if he wakes after an hour or two, I know he is not hungry and rather just woke up and needs to go back to sleep. I started tracking his sleep patterns and found (when he was taking good naps of 1 1/2 to 2 1/2 hours) that he could only be awake for 1 1/2 hours then he would get overtired and be impossible to sleep. Now he can only go about an hour and then has to nap again since he only naps for 30 minutes. So you might be missing your "window" and he might be overly tired then and not go to sleep. Also are you doing the 12 hour thing? Weissbluth says 12 hours from when they wake up (at your son's age) they should be going down for the night. So if he wakes at 6 for the day (and then should do a little sleep of maybe 45 minutes or an hour after he wakes up as one previous post said) he should be going down for the night at 6pm. Again, I learned so much about what to expect about sleep from Weissbluth, but I just don't love his techniques (and his book is horribly organized and at times hard to follow). So you might want to request that from your local Chic. Public Lib branch and at least read it for that. Try requesting the other books too if you think you don't want to do CIO. I have friends that swear by it. I think it works and most of the time the results are very fast a couple days to a week and they are sleeping through the night (but Weissbulth says you should not do CIO until 4 months and Ferber says 6 months), it just would be impossible for me to handle it.
Best of luck!!
S.