Dc3 is 15mo and still suffers from wind at night at times. We finally got a dairy intolerance diagnosis after we started weaning (dismissed up to that point due to bf!).
Does he have any other symptoms? Ds and I have both been dairy free for 6 months, and a marked improvement, but sadly the crap sleep patterns were already there, so he's used to being fed back to sleep / to soothe his tummy.
There are still a few foods he seems not to tolerate well, and I haven't managed to work them all out yet, but he has a bad night once in a while, where he wakes screaming, kicking legs, arching his back, literally trying to kick it out! - it's always been trouble with bottom wind, never a problem with burps. I know when he's had something as he has eczema just on his face, which flares up.
On our hit list are- grapes, bananas, baked beans, poss some of the windy veg, tomatoes, nuts (exposed through bf mainly). he can tolerate small amounts now of some.
Forgive me if this is a very basic suggestion, but do you try all the cycling legs in air, pushing legs into tummy and straightening, wind relieving type exercises? At 18mo you could probably make them a bit fun and it might help get some wind out?
You have my sympathies, I have googled this and searched on here for the last 15months! Nothing worse when they're screaming in pain, staring at you as if to say make it stop!