I have just been through the exact same thing with my 4 month old. I finally rang Plunket, what they told me was very simple, but being sleep deprived I hadn't thought of it.
We were trying to rock, swing, nurse our DD to sleep, the more we did the more upset she got. I tried wind stuff, teething stuff, even panadole, but it has worked out the more we were doing to her the more overtired she was getting. Plunket said that some babies simply need to switch off by themselves. So at the first sight of her tired sign, which for her is she starts to 'talk', I wrapped her up, took her into her room and put her into her cot. I gave her the dummy and just left me hand on her chest. She fussed a bit, but never cried, this went on for about 10 mins, then she just stared into space and then 5 mins later she was asleep. She woke again after 40 mins, I just went in and put my hand on her again and gave her the dummy and this time it took about 20 mins. But not once was there any crying or screaming. I actually cried cause it was so simple!!
I hope this helps you as well and over time we end up with wonderful sleepers!!