i had the same problem and i just used the sling whenever i needed to to settle them (even in the middle of the night sometimes!) and then whenever they were ok i would try to settle in the cot.
also when they were in pain for wind etc i would give nappy off time and help move their legs around a bit which seemed to help. Also have you tired looking at your diet if you're still breastfeeding? things like chocolate, tomato, brocolli etc caused heaps and heaps of belly ache with both my ds and dd - so try cutting all that stuff out.
oh and also go to a chemist and try and find mariners infant mixture. it's all natural and you give it before feeds. at first i was reluctant to try it but it worked brilliantly! but you have to keep giving it regularly for it to really help. after 1 day of changing my diet and giving the mariner mixture i noticed a huge change and the awful grunting noises stopped too.
hope that helps - but remember it really really really does get better!