i know how you feel! ::)my lo is nearly 5 months and has been waking habitually at around 2am and then 5ish for a while. we have found that wake to sleep seems to be helping. i set my alarm for around 1am and go in and stir him by stroking his head and slipping his dummy in. this has helped when he starts to stir at 5/ 5:30 as well.
also, i don't know if it helps you, but i feed my wee man at 7am, 11am, 3pm and then his bedtime routine is bath at around 7pm and his feed right before he sleeps. (he gets his dreamfeed at 10:45pm.) he also naps for 1 1/2 hours in the morning, then 1 hour and then 45 mins- 1 hour for the two afternoon naps. maybe if your lo had a longer nap in the afternoon and an earlier dreamfeed it could help, as 11:30 seems very late (you may be breaking his deep sleep)?
i hope this helps even a little, as i know how frustrating it can be!