Anyone have advice for a 4 month old who is awake every 15 mins from 2am to 6am?

[peapod987]

My 4 month old won't sleep properly at night. We're giving baby rice at 5/6ish with a feed and a 10.30pm night time drink feed (with rice and oats in) and have been advised not to feed at 3am anymore. She uses a dummy and thats what I'm replacing every 10 - 20 mins in the night. She doesn't even finish half her 6.30 -7am feed so can't be hungry all night. Know the dummies creating a problem but after 2 hrs of non stop screaming the other night I've gone back to it. I've just started the Gina Ford routine which works in the day (so she's not sleeping too much in the day) but am desperate for sleep at night time. Any advice very welcome.

Forgot to add that ds turned out to have severe colic, i was breastfeeding during the day but giving formula at night (to help with recovering from being anemic), and ds turned out to be allergic to the formula, so we got Nutramigen - hypoallergenic formula - on prescription from the doctor and this cured him of waking in pain almost instantly.
also weaning him off the dummmy only took 1 day, it was far easier than i'd anticipated....