My DS slept from 9pm- 5am, and then again until 9am last night/today. That's not as good as usual, but it's ok-ish. It's usually around ten hours but I'm not sure why sometimes it's longer than other times IYSWIM.
I concentrated on what I did so that i could run through it today to see if it helps you at all.
Bathed him, fed him an hour early (he didn't take it all), put him down while he was still giggling and happy. Turned the light out, and walked away. He coo'd a little and then went quiet, so I went in to check and he was fast asleep. I checked every 15 minutes until 10 o clock, and then went to bed myself and he didn't even stir whilst I changed into my nighty and things. I heard him chatting to himself at 3 for a couple of minutes, then he went off by himself, and he wanted a feed at 5.15, so I fed him, changed him, put him straight back down, no playing. He then slept until 9 and woke up giggling and chatting, he wasn't even hungry.
I think the main thing I do is I don't fuss with him at bed time, just lay him down, kiss him, light out. And when he get up in the night, I feed him, change him, straight back down.
I am lucky enough to have a very good baby though. I feel for you as I found it so difficult when he was feeding every 3 hours at night, and had colic so we he'd feed for about an hour, wind for an hour to an hour and half, put down, then time for a feed again.
You can only do your best and keep trying things- some babies just don't sleep well.
Hang in there!