Weird sleep-habits for 6-month old baby?

My son has always been a light sleeper, which I usually just ignore. But nowadays I'm concerned that something is actually troubling him. Every 30 minutes (at night) he'll start tossing and turning back and forth, throwing his arms and head this way and that way and basically needs his pacifier or my in his mouth to fall asleep. Then he settles immediately. Then this starts half an hour later again. Why can't he sleep deeply? Any chance he has stomach cramps? I've tried eliminating different things in his diet with no luck. I know adults can also be fidgety sleepers, but I'm surprised a baby can't sleep soundly for even an hour without me putting something back in his mouth to chew. Any ideas?