DD is five months old. 'Usual' sleep pattern of 6pm-5am from 8 weeks up until three weeks ago which we took for granted was lovely.
He's started waking constantly through the night. He goes down at six without any faffing, but then wakes at 11pm, 1am, 2.30am, etc. Sometimes his dummy will settle him straight away, other times he'll flail around for ages and only go back to sleep after he's downed a bottle. He doesn't really make a noise though; it's not like he's waking up crying 
He has cut two bottom teeth. He's formula fed and we haven't started weaning him yet. He sleeps for around 3 hours during the day, more if we're out and about.
As title suggests I'm baffled as to whether this is the four month regression, more teething, a growth/developmental spurt or a sign that he's hungry (although I'm extremely dubious that solids will solve this issue). I'm guessing it's a delightful combination of the above.
I'm going to try a dreamfeed tonight and see if it makes a blind bit of difference.
Anyone been through the same or able to offer words of wisdom?