DS is waking up at best every 2 hours, at worst every 15 mins at night 
He doesn't cry as such, but he will lie there groaning and thrashing his legs and turning his head because he desperately wants to sleep but can't seem to. If I feed him or DH rocks him he'll instantly calm (90% of the time) and then we can put him down and he sleeps. But often 10 - 30 minutes later he's grumbling again.
Should we just leave him to grumble? I'm afraid it'll wake him up even more if he just lies there trying to sleep but not being able to.
We sometimes leave him to grumble for 5 minutes but he never manages to self settle. Most nights he self settles for the first time, i.e. I feed him and he dozes off but me getting up to put him in his cot wakes him up and then he goes to sleep by himself.