Hi A.,
I have the EXACT same problem, and I think I bought all the sleep book on the market! Like you though, all the solutions provided have to do with teaching babies how to fall asleep on their own...which mine does without a problem. I nurse him, put him down fully awake, and he "talks" to himself, plays with a blanket...etc, usually for about 5 minutes or so and then peacefully falls asleep.
However, in the middle of the night, if I don't go in to nurse him, there's no going back to sleep. He'll cry and cry and cry. So weird. (Oh and he also wakes up at different times every night, so the techniques to changing the "habitual wakings" outlined in some books - like waking him an hour before he usually wakes up...etc. - can't be applied either !)
Our first son had horrible sleep associations, we had gotten into the habit of rocking him and rocking him to sleep and of course had to re-do it everytime he woke up (which I realized was out fault). But Jacks, our second, doesn't need one bit of help going down at naps or in the evening. So this is just so confusing.
The only thing I can tell you is that he is now 7 months old, and went from getting up 2 (sometimes 3 times) to nurse, to only once over the last 2 months...without me doing anything different (i would still nurse him every time he woke up). And over this past week, he's actually slept through the night (12+) hours, twice. We're still not "there yet" :) but I feel it's an improvement. I am still completely clueless as of why it has changed (and like your baby, mine definitely doesn't seem to need those extra feedings at night) but it has.
So hang in there! I know how you feel. It's so confusing and their behavior go against everything outlined in books, and it would just drive me nuts, not knowing what to do.
In the meantime, if you find a solution, please let me know !!!!
Good luck !
C.