Is he teething or unwell at all?
The only other thing that springs to mind is trying to get more milk into him during the day - 3 feeds doesn't seem like much at 7 months, but I guess they're all different.
In our case it was a mixture of settling (when teething or unwell or otherwise out of sorts) and hunger. DS was 18 months before he could go all night without eating anything, but it was just one feed if he wasn't sick or teething.